Are nitrates and phosphates bad for fish?

[JamesC]

In a UK fishkeeping mag a regular contributor has started a heated debate about whether adding nitrates and phosphates are harmful to fish. He is of the opinion that adding NO3 and PO4 is harmful to fish and we shouldn't do it. His reasoning behind this is that in natural rivers, lakes, etc these levels are very low and we should try to reproduce the same conditions in our tanks. Also that where there are high levels of nitrates there are large algae problems and limited life.

Now I'm no expert on this so can't comment on whether NO3 and PO4 is dangerous to fish but what I can say is that I've noticed no ill effects on the fish and shrimp in my tank that has been running EI for a couple of years now.

So are we keeping are fish in polluted water or not is my question.

James

 

[VaughnH]

We are definitely not duplicating natural growing conditions for our plants. Why would we want to do that? We are growing a variety of plants in a small glass tank, indoors, with weak light compared to sunlight, with a substrate that isn't mud, and we jam the plants together, prune them to the shape we like best.

The fertilizers we add are in very small concentrations, but we try to keep the concentrations steady, where in nature they vary as conditions vary. Our fish survive very well, reproducing even, and, although they can't talk, they sure appear to be content with their lives.

So, in my opinion, we are keeping fish and plants in very nice conditions.

 

[Henry Hatch]

I have had tanks with phosphates in excess of 10 ppm ( not on purpose) and I have a non co2 plant tank with nitrates in excess of 40 ppm. I think at really high levels fish will react to nitrates. I have never seen adverse affects to phosphates at any level.

Henry

 

[JamesC]

I agree I've never seen any problem with my fish or shrimps but that doesn't mean it isn't bad for them. People smoke which is very bad for them but they usually don't show any outward signs for many years. Reason I ask is that governments set limits on nitrate in our tap water (10ppm in the US I believe and 50ppm here in the UK) I presume because they believe it is bad for us. Would this also not be true for fish?

James

 

[Tom Barr]

In a UK fishkeeping mag a regular contributor has started a heated debate about whether adding nitrates and phosphates are harmful to fish. He is of the opinion that adding NO3 and PO4 is harmful to fish and we shouldn't do it. His reasoning behind this is that in natural rivers, lakes, etc these levels are very low and we should try to reproduce the same conditions in our tanks. Also that where there are high levels of nitrates there are large algae problems and limited life.

Now I'm no expert on this so can't comment on whether NO3 and PO4 is dangerous to fish but what I can say is that I've noticed no ill effects on the fish and shrimp in my tank that has been running EI for a couple of years now.

So are we keeping are fish in polluted water or not is my question.

James

Nothing wrong with asking such a question.
Instead I'll give real data and test.
Then you may draw your own conclusion.

I'm going to make an assumption that this person is a standardized hobbyists making this argument. I've heard this same argument perhaps 100X prior.
Note, I have no knowledge of what was really said etc.

Issue 1#
He first assumes that KNO3 derived NO3 is equivalent to NO3 derived from fish food, transformed into fish waste, which is then transformed into NH4, which is further transformed into NO2=>NO3 Obviously, NH4 etc is not the same as NO3.
Bad assumption.

2#
He also further assumes that these various transformations in the tank plays no role and that the NO3 he measures is all inorganic like that of KNO3.

3#
The NO3 can be added via KNO3 to test this and then you can progressively overload and small tank by slowly adding small fish, one by one till you get a toxic response.

4#
I've gone for extended periods, several months with Discus and with south American wild fish such as catfish, tetras and so called sensitive fish as well as shrimps. I've bred discus as have many others in such tanks, maybe just lucky each and every time?

5#
Shrimps are the most sensitive based on what I and others have noted in response to NO3 and NH4. How would I know this without testing it myself personally and monitoring? Therefore they make the most ideal candidates.

6#
I added NO3 using KNO3 to a very well stocked tank for 3 days at 160ppm of NO3.
I manged to geta LD 50 of shrimp(Amano shrimp, C japonica) after 3 days. No fish got sick or appeared stressed surprisingly.
I tested it again and with other fish, again, no response noted.
Shrimp seem to have issues at 120-160ppm range.
60-80 ppm did little over 2 years in a 20 gallon shrimp tank.
Some derived NO3 was from food in that tank as well as the others, but most of the NO3 is still from KNO3.

7#
I knew 70-80 ppm did not harm, but even at very high extremely levels, far outside those produced usign even heavy EI, there is no such response.
Altum angels are often considered sensitive, a school of 62 are present in a client's tank using plain full EI. They are in obvious excellent health near as anyone can tell, they are not scared, they eat well, they have grown well.

8#
PO4 has never once been shown nor implicated as a toxicant in an aquarium that I am aware of. See more below.

9#
As far as sublethal impacts on fish you cannot see, well, I know the folks here at UC Davis that work specifically on this question, they can measure potential issues, but not with fish very well. you need to dissect and do other methods to measure this, measure HSP70's proteins etc and other stress proteins to see.
I've never seen one study done on aquarium fish to this extent using any of the standard method utilized in the research.

10#
If he or others have, post the reference.

So this nor anyone really has the information to answer this for every species of fish we keep, that much is clear, so this person is really going way out on a limb in the speculation and seems to have very little experience or background actually measuring NO3 accurately, let alone applying KNO3 in a manner to see if toxic effects of any sort, lethal or sublethal are evident.

Raising the question is good, but I've met more than my share of fear and doom mongers in my life. The real question is it an issue as claimed?

Just like PO4 = algae baloney that was jammed down the throats of aquarist, and that high trace Fe causes algae etc, these turned out to be myths.
I've heard the BS before.

What is more important and helpful to the hobby is not mere repetition of such dogma, rather, actually doing something and trying to answer such questions and applying it.

Many folks that like to debate on the web sit at the computer too much and do not actively try methods out, they do not seek out the research to and do such testing methods.

I get sick of those clowns, truth be told.
Blow hards that never offer anything new or useful, I'm not saying that this is what the person is or not, I have no idea what specifics where said, I am generalizing based on a 100's of similar complaints I've retorted in the past.

Same old thing 101 times.

10#
Fat healthy growing fish, that bred etc, sensitive species identification and specific information like I give(concentration, dose, specific conditions and type of treatment: KNO3, many years of dosing with both plants, KNO3/fish etc.

11#
You are welcomed to believe what you wish.
I can answer most of this persons criticisms, question is, can he answer mind and show otherwise.

Neither of us are ever going to really get at the sub lethal effects. At least not for a long time.

12#
How do we know if the fish did not die from natural causes, disease, some other confounding parameter? If the fish lives and grows, breeds and is fat and happy compare to an untreated fish, then obviously the sublethal effect would appear not to be that significant. you have to have some way and method to measure and quantify these effects. It's hard to say, but in respect to some organisms, they are finding some decent methods/ways to answer this.
That in itself in an entire topic.

13#
So "no impact" is rather easy to show, he needs to show that the causation is due solely to NO3 and PO4. That is much harder.

I bet a wooden nickel he cannot do that and rule out the other confounding factors.That is much more difficult. I know and the fish and aquatic animal researchers here know this.

He can piss and moan all day, but unless he does the work, has some sort of support in the primary research as applied to our case, he really does not know and can barely even speculate, not having even done even any sort of test or thought things out about what might play a role using KNO3 etc

Contrast that with myself.

SeaChem and many other companies have long sold PO4 based acidifyers that are added way above 5-10ppm. Do you think they would use and sell these for the last 30-40 years if they really where lethal? Perhaps Westinghouse sold PCB's for years, they sold DDT etc, but today we do have a fair amount of test methods available to avoid such past mistakes.

If someone is too lazy to do the work well.............they need to shut up and stop basing their argument on guessing and fear.
They are 10 years behind to even catch if they did start testing, so I have a lot of dosing comparision in the my personal background as well. I started workign at a LFS 30 years ago. Been very active, more so that about anyone on the web about plants for a decade.
I got the practical experience.

Just show them nice tank after nice tank, lots of healthy breeding fish, lots of nice plants etc.

Then laugh at their so so tank with algae.

That's gotta hurt
But be nice and ask them basic questions.

Have they tested it with.without KNO3 or not?
How much was added and for how long?
What critters where used?
What types of impacts did they look at/for?
What test methods did they use the measure the NO3/PO4?
Did they make a calibration curve for their test method?
Where plants added?
Where other parameters that might influence results accounted for adequately?
Fish health and food/feeding?
Tap water/make up water?

If the fish are fine, grow well, bred, appear to have no discernible impact after 10 years on 1000's of tanks, what are the chances that this person is correct?
I do not need a control to test that, the fish are fine, actually better, than the controls with the folks that have no plants.

Ask him when the last time he need medication. I have not needed any for 15 years since switching to planted tanks mainly. Fish do not get sick.

Maybe I'm just really really really lucky, but you can decide for yourself.
Note, none of what I've said is based on anything this person you refer to has stated or said, just what you have told me, I've addressed the normal stuff folks often ask and their arguments as an assumption.

So if this guy comes here complaining, he knows I've made that assumption, I know nothing


Regards,
Tom Barr

 

[Tom Barr]

I agree I've never seen any problem with my fish or shrimps but that doesn't mean it isn't bad for them. People smoke which is very bad for them but they usually don't show any outward signs for many years. Reason I ask is that governments set limits on nitrate in our tap water (10ppm in the US I believe and 50ppm here in the UK) I presume because they believe it is bad for us. Would this also not be true for fish?

James

This is an excellent point, so what types of tools would you use or consider using to measure and quantify such a possible issue?

NMR in vivo studies have works very well with shellfish and abalone, but it's harder to say what impact these effects have at the ecological scale or for an aquarium.

Heat shock proteins (HSPs) have been used to measure stress due to temps. They measure quanatitively the amount of shock protein produced in response to a treatment by using extracts via Western Blot and then perhaps PCR amplification for the mRNA using a northern blot to see if there is a correlation or any post translational mechanisms etc.

Dissection and measuring things like egg counts and viability, various specific tissues for effects on protein synthesis, stress proteins(P450's etc), conjugates etc are also done as well.

Still, how bad is this to be cause for concerned in our aquariums?
That is the larger issue
after a decade, I have not seen anything that suggest so, even if it did appear at say 60-80 ppm NO3, it's easy to reduce that using plants and dosing less.

NO2-

AFS Online Journals - Toxicity of Nitrite to Fish: A Review

NO3-
Long term studies suggest levels above 100ppm are problematic. But I've never suggested to add that much and this assumes a natural source, which may be derived vai NH4 loading.

CSA

Here's some basic stuff on NO3 and support my observations about 2-3x above the limit I stopped at:

SETAC Journals Online - ACUTE AND CHRONIC TOXICITY OF NITRATE TO FATHEAD MINNOWS (PIMEPHALES PROMELAS), CERIODAPHNIA DUBIA, AND DAPHNIA MAGNA


Contrast NH4/NO2(which is virtually always absent in planted tanks all the time) which is what is likely the problem with non KNO3 derived sources of NO3

AFS Online Journals - Acute Toxicity of Ammonia and Nitrite to Cutthroat Trout Fry

Background research might help folks figure things out a little bit better and form and reasonable conclusion based on what is know and what have/can do to answer the question.

Further:

Trout:
Un-ionized ammonia (NH3; 0.125 mg/L as N) was about six times more toxic than nitrite (0.79 mg/L NO2-N) and about 13,300 times more toxic than nitrate (1,658 mg/L NO3-N). (Buhl and Hamilton, 1998)




Regards,
Tom Barr

 

[Tom Barr]

More about how to measure sublethal:

SETAC Journals Online - CHANGES IN CELLULAR ENERGY BUDGET AS A MEASURE OF WHOLE EFFLUENT TOXICITY IN ZEBRAFISH (DANIO RERIO)

SpringerLink - Journal Article

http://www.rsmas.miami.edu/groups/grosell/PDFs/2005 Tomasso & Grosell.pdf

Blackwell Synergy - J Appl Ichthyol, Volume 21 Issue 5 Page 451 - October 2005 (Article Abstract)

http://www.cababstractsplus.org/google/abstract.asp?AcNo=20043063545

You really have to ask, the NH4 and NO2 are obviously extremely toxic, 1000X more so in most cases, why would we want to add these via fish waste at high rates for the plants?

Maintaining lower levels of fish stock and high plant biomass with good moderate KNO3 dosing, say about 30ppm etc works well.


Got high NO3 tap?
Use that and make sure it's stable and add K2SO4 in place
You can also filter and reconsititute with KNO3.

Maybe I am all wrong about the fish waste derived fraction and the NO3 is merely correlation, but not what is the real rish to fish health unless it's extremely high?

But .......based on the overwhelming evidence as well as years of practical experience, that is what is not what is suggested.

This guy would get a debate beating if he wants to tangle on this topic.
Slapped with a mullet

Regards,
Tom Barr

 

[Tom Barr]

He is of the opinion that adding NO3 and PO4 is harmful to fish and we shouldn't do it. His reasoning behind this is that in natural rivers, lakes, etc these levels are very low and we should try to reproduce the same conditions in our tanks. Also that where there are high levels of nitrates there are large algae problems and limited life.
James

We are not lake and river keepers are we?
That is not true that these levels are low in all rivers/lakes etc.

Nor is there any correlation between NO3/PO4 and algae in subtropical and tropical shallow lakes with aquatic plants (See Bachmann et al, 1984-2007, lots of evidence surveying 100's of lakes).

These are lakes much more like out planted tanks than any other.
So this applies much better.

Fish production is very high, the best fisheries for bass in the world.
Why? Plants and moderate warm temps, ample food etc.

So there is massive life and no algae, these lakes are gin clear and you can see them in the water.

Poor methods have promoted this myth, but if you add more nutrients to a wetland/shallow planted lake, all you get is more weeds, anyone that deals with aquatic weeds knows this, the aquarist are the ones that are clueless, at least some seem to still be even decades later.

regards,
Tom Barr

 

[Tom Barr]

So are we keeping are fish in polluted water or not is my question.

James

Polluted is a political word in it's use here.
The answer is really like this: do you pollute the soil when you add fertilizer for garden?

Why is that different here?
Because of the fish?

What is pollution?

How does one define that and what would consititute polluted tank?
Are Amano's tank's pollute?
He adds lots of nutrients, ADA AS is loaded with NH4, folks do not add any fish for several weeks due to that, fish will pick at the grains that are loaded, mud has lots of nutrients, plants export nutrients/pollutants out of the soil into the water, fish eat plants with lots of NO3/NH4/PO4 etc.

Some say pollutant, some say fertilizer.

Just because you maintain non limiting conditions for the plants does not suggest it's to be called a pollutant.

That's hyperbole. It's not supported in anyone' observation on our fish nor sub lethal effects is just a response to their belief, if they feel passionately about this topic, they should start proving that it's a real problem rather than preaching horrors of NO3/PO4 and doom.

Just keep showing them the nice tank you have.
Show them the fish, ask why are not your fish harmed year after year?
Ask them if they have years of success with their fish.
You lead by example.

Regards,
Tom Barr

 

[Tom Barr]

If anyone has a moment, reading this might help if forwarded to Jeff over at PFK's.

I read a few of the threads.
He's asking for this references etc and I have some that explain and support my contention and refute his so called experts.


The tech version:
http://fishweb.ifas.ufl.edu/Faculty Pubs/CanfieldPubs/macrophyte.pdf

and the more general reading version:

http://fishweb.ifas.ufl.edu/Faculty Pubs/CanfieldPubs/Aquatics2004LR.pdf

Now come back to fish and so called polluted waters:
http://fishweb.ifas.ufl.edu/Faculty Pubs/CanfieldPubs/TrophicState.pdf

This suggest that more plants/nutrients are correlated positively with more fish biomass as well.

Canfield, D.E., Jr., K.A. Langeland, M.J. Maceina, W.T. Haller, J.V. Shireman, and J.R. Jones. 1983. Trophic state classification of lakes with aquatic macrophytes. Canadian Journal of Fisheries and Aquatic Sciences 40:1713-1718.

Canfield, D.E., Jr., J.V. Shireman, D.E. Colle, W.T. Haller, C.E. Watkins II, and M.J. Maceina. 1984. Prediction of chlorophyll a concentrations in lakes: The importance of aquatic macrophytes. Canadian Journal of Fisheries and Aquatic Sciences 41:497-501.

Canfield, D.E., Jr., J.V. Shireman, and J.R. Jones. 1984. Assessing the trophic status of lakes with aquatic macrophytes. pp. 446-451. Proceedings of the Third Annual Conference of the North American Lake Management Society. October. Knoxville, Tennessee. EPA 440/5-84-001.



Canfield, D.E., Jr. and R.W. Bachmann. 1981. Prediction of total phosphorus concentrations, chlorophyll a and Secchi depths in natural and artificial lakes. Canadian Journal of Fisheries and Aquatic Sciences 38(4):414-423.

Canfield, D.E., Jr., J.R. Jones, and R.W. Bachmann. 1982. Sedimentary losses of phosphorus in some natural and artificial Iowa lakes. Hydrobiologia 87:65-67.

Canfield, D.E., Jr. 1983. Prediction of chlorophyll a concentrations in Florida lakes: the importance of phosphorus and nitrogen. Water Resources Bulletin 19:255-262.

Canfield, D.E., Jr. 1983. Impact of integrated aquatic weed management on water quality in a citrus grove. Journal Aquatic Plant Management 21:69-73. Canfield, D.E., Jr. 1983. Sensitivity of Florida lakes to acidic precipitation. Water Resources Research 19:833-839.

Canfield, D.E., Jr., M.J. Maceina, L.M. Hodgson, and K.A. Langeland. 1983. Limnological features of some northwestern Florida lakes. Journal of Freshwater Ecology 2:67-79.

Canfield, D.E., Jr. and L.M. Hodgson. 1983. Prediction of Secchi disc depths in Florida lakes: Impact of algal biomass and organic color. Hydrobiologia 99:51-60.

Canfield, D.E., Jr., R.W. Bachmann, and M.V. Hoyer. 1983. Winter salt freeze-out in hardwater lakes. Limnology and Oceanography 28:970-977.

Canfield, D.E., Jr., K.A. Langeland, M.J. Maceina, W.T. Haller, J.V. Shireman, and J.R. Jones. 1983. Trophic state classification of lakes with aquatic macrophytes. Canadian Journal of Fisheries and Aquatic Sciences 40:1713-1718.

Canfield, D.E., Jr., M.J. Maceina, and J.V. Shireman. 1983. Effects of hydrilla and grass carp on water quality in a Florida lake. Water Resources Bulletin 19:773-778.

Langeland, K.A., D.L. Sutton, and D.E. Canfield, Jr. 1983. Growth response of hydrilla to extractable nutrient in prepared substrates. Journal of Freshwater Ecology 2:263-272.

Canfield, D.E., Jr.1984. A survey of sodium and chloride concentrations in Florida lakes. Florida Scientist 47:44-54.

Canfield, D.E., Jr. and C.E. Watkins II. 1984. Relationships between zooplankton abundance and chlorophyll a concentrations in Florida lakes. Journal of Freshwater Ecology 2:335-344.

Maceina, M.J., J.V. Shireman, K.A. Langeland, and D.E. Canfield, Jr. 1984. Prediction of submersed plant biomass by use of a recording fathometer. Journal of Aquatic Plant Management 22:35-38.

Canfield, D.E., Jr., J.V. Shireman, D.E. Colle, W.T. Haller, C.E. Watkins II, and M.J. Maceina. 1984. Prediction of chlorophyll a concentrations in lakes: The importance of aquatic macrophytes. Canadian Journal of Fisheries and Aquatic Sciences 41:497-501.

Canfield, D.E., Jr., S.B. Linda, and L.M. Hodgson. 1984. Relations between color and some limnological characteristics of Florida lakes. Water Resources Bulletin 20:323-329.

Canfield, D.E., Jr., J.V. Shireman, and J.R. Jones. 1984. Assessing the trophic status of lakes with aquatic macrophytes. pp. 446-451. Proceedings of the Third Annual Conference of the North American Lake Management Society. October. Knoxville, Tennessee. EPA 440/5-84-001.

Canfield, D.E., Jr., M.J. Maceina, F.G. Nordlie, and J.V. Shireman. 1985. Plasma osmotic and electrolyte concentrations of largemouth bass from some acidic Florida lakes. Transactions of the American Fisheries Society 114:423-429.

Canfield, D.E., Jr., S.B. Linda, and L.M. Hodgson. 1985. Chlorophyll-biomass-nutrient relationships for natural assemblages of Florida phytoplankton. Water Resources Bulletin 21:381-391.

Canfield, D.E. Jr., K.A. Langeland, S.B. Linda, and W.T. Haller. 1985. Relations between water transparency and maximum depth of macrophyte colonization in lakes. Journal of Aquatic Plant Management 23:25-28.

Shireman, J.V., M.V. Hoyer, M.J. Maceina, and D.E. Canfield, Jr. 1985. The water quality and fishery of Lake Baldwin, Florida: 4 years after macrophyte removal by grass carp. Proceedings of the Fourth Annual Conference and International Symposium of the North American Lake Management Society. October 16-19, 1984. McAfee, New Jersey.

Shireman, J.V., D.E. Colle, and D.E. Canfield, Jr. 1985. Efficacy and cost of aquatic weed control in small ponds. Water Resources Bulletin 22:43-48.

Hoyer, M.V, D.E. Canfield, Jr., J.V. Shireman, and D.E. Colle. 1985. Relationship between abundance of largemouth bass and submerged vegetation in Texas reservoirs: A critique. North American Journal of Fisheries Management 5:613-616

Hoyer, M.V. and D.E. Canfield, Jr. 1985. Plant biomass in several Florida rivers. Aquatics 7:16-17.

Hodgson, L.M., S.B. Linda, and D.E. Canfield, Jr. 1986. Periphytic algal growth in a hypereutrophic Florida lake following a winter decline in phytoplankton. Florida Scientist 49:234-241. Hoyer, M.V. and D.E. Canfield, Jr. 1986. Surface area of aquatic macrophytes. Aquatics 8:26-27.

Canfield, D.E. Jr., and M.V. Hoyer. 1988. Influence of nutrient enrichment and light availability on the abundance of aquatic macrophytes in Florida streams. Canadian Journal of Fisheries and Aquatic Sciences 45:1467-1472.


Now not one of these researchers thought I was the least bit crazy with what I noted in aquariums with lots of plants, nor did Troels from Tropica nor Dr Ole Peterson from Denmark.

The researchers agree, it's the hobbyist that have the issue and the block in the thinking. 95% of the algae related issues are due to CO2, not NO3/PO4 etc.

When the adequate levels of CO2, generally about 30ppm or so, are met and stable over the light period, then algae is no longer an issue when you add fertilizers.

To someone that is not aware of that, adding NO3/PO4 to a poor CO2 plant tank will get the predicted bloom and with good reason, the low levels of CO2 are not enough to support full plant growth. When PO4 and or NO3 is limited, that down regulates CO2 demand. so your plant needs less now due to a secondary PO4 limitation.

This dramatically slows the growth down.
That slows the CO2 demand down as well.

If you remove a strong PO4 limitation by adding PO4 fertilizer, then the CO2 uptake will sky rocket.

So 10ppm might have done it before, now without any other limitation to CO2 uoptake/demand by the plant, it is free to gobble up as much CO2 as it can.

So this rules out all the nutrients as being a cause to slow plant growth. Then it's on to the next issue, getting good CO2 so you can objectively measure and judge the nutrients and lighting indepdently.

If you have poor CO2 at high light and want to vary the PO4 levels around, that will confound the method and reasults.

That's bad data. But if you are not aware of this effect or do not account for it reasonably well with a good method to measure CO2 etc, then how would you know?

You wouldn't.

Regards,
Tom Barr

 

[Tom Barr]

I'm sitting in on a class with CR Goldman this spring.

He's published things with another mentor:
. Bachmann, R. W. and C. R. Goldman. 1965. Hypolimnetic heating in Castle Lake, California. Limnol. Oceanogr. 10:233-239.

These guys just keep teaching

http://fishweb.ifas.ufl.edu/Faculty Pubs/HoyerPubs/HoyerMacrophytes.pdf

http://fishweb.ifas.ufl.edu/Faculty Pubs/Cichra Pubs/CichraRainbowRiv.pdf

You want tropical fish health folks?

Ruth Francis-Floyd

She is awesome.

If you are interested, she offers a 6 day course:
UF - Aquatic Medical Education

Come down and then I'll drag you around all the planted rivers and cess pools.

Jeffrey E. Hill

Dr Hill has a good resume here as well.

But what do I know when seeing if something is going to harm fish or not?
Disease?

I'm a plant guy, but I do have to address other critters in these systems as well, they are linked after all.

Read all this and you will have a different view about what is known.

Also, this months BarrReport is about to be sent out and done and it addresses fish waste namely , how we model a fecal pellet in reltionship to plants and measurements/toxicity etc.

Regards.,
Tom Barr



Regards,
Tom Barr

 

[barbarossa4122]

Excellent, informative thread. My no3 concerns are completely gone. Thanks Tom

PS. Glad I subscribed.

 

[Tom Barr]

I still have never found any toxicity ppm's for PO4............

Regards,
Tom Barr