Question on Alkalinity and KH

[rrguymon]

Ok let me start by saying the KH to PH relationship in my tank seem really messed up. I have had calculated readings of over 100ppm of co2 and the fish are fine and dandy and the plants are growing but not much pearling.

I have started to do some research and would like someone to confirm if I have wandered upon the reason. Kits measure total alkalinity but the only part of the alkalinity that effects ph co2 relationship is Bicarbonate. My total alkalinity per the water department is 116 and the bicarbonate is 46. 116 would equal 6.5 kh 46 would = 2.6kh. I guess in most cases the majority of the alkalinity is made up of bicarbonate, but in my water bicarbonate is less than half.

My KH test kit shows KH of 6.5 to 7. I started shooting for a ph around 6.7 based on the kit. At 6.7 it seemed like there was little co2 in the water. I think I should be using the 46ppm number as my kh which would put my target ph at 6.3 or so.

I am now at 6.3 for ph the fish are doing wonderful and that plants are pearling much better. For the record 6.3 = 39 ppm co2 if the kh is really 2.6 or 98 is the kh is really 6.5. Right now I tend to believe my co2 is much nearer the 39 number.

Thanks

Rick

 

[rrguymon]

Re: Question on Alkalinity and KH

Guess no one knows about alkalinity and KH. I think I will get me a chemistry book. I am also going to try and find out what the other bases are in my water besides the bicarbonate. I would really like to be able to measure the bicarbonate too.

I live in ABQ NM and the Rio Grand river runs North and South through town. The water department web page has a map utility that lets you select the different water zones in the city and view the water report. I find it interesting that all zones on the east side of the river have almost all the alkalinity made up from bicarbonate an all the zones on the west side of the river only have about half the alkalinity made up from bicarbonatites.


Thanks Rick

 

[Tom Barr]

Re: Question on Alkalinity and KH

You raise a good question about the alk, it might be from another buffer, borate buffer systems are present in marine water, it's fairly low and does not impact the Carbonate system that much.

Based on your tap water's alaysis, I'd have to say you do have alk issues and that the pH KH chart may present issues.

I wonder if this is why some folks also have issues with the ph/KH chart as well. NM/AZ and the southwest have some odd minerals and borate desposits that can cause bicarb alk issues.

Tannins, poor measurement error etc can cause some issues, but I think we see a lot more than any one single reason would suggest.

I would go with the bicarb alk only for the CO2 measurement.
That would give you the range of CO2 that seems appropriate 39ppm.

Good work BTW, few folks would catch what you did.
I'd say you have it figured out.

Regards,
Tom Barr

 

[Laith]

Re: Question on Alkalinity and KH

Yes, this is quite interesting. How does one measure only the bicarb?

 

[matpat]

Re: Question on Alkalinity and KH

Ditto Laith's reply.

Not trying to hi-jack the thread but I may be in a similar situation. I figure with a KH of 4.5 and a pH of 6.1, my fish should all be dead! This may also explain why my plants don't pearl when my CO2 is around 30-40ppm!

Definately a good catch, thanks Rick!

 

[Tom Barr]

Re: Question on Alkalinity and KH

Well, NM, AZ etc have high borate deposits in lake beds etc after the SW USA became hotter and drier over the last 15,000 years. Death Valley use to be Silver lake, a massive lake nearly the size of one of the great lakes, Lake Madix further south along the the ancient silver river was also huge, the great salt lake use to be truely massive as well, easily as big as a great lake.

My point here is that non bicarb alk is rare, but this level varies to some degree for folks in the SW. 20 mule Team borax is from Death Valley originally.

I certainly do not think it represents most of the CO2 related issues folks see, but things like measurement error, complacency, electric stray current, tannins, etc are more to blame in general.

Regards,
Tom Barr

 

[Tom Wood]

Re: Question on Alkalinity and KH

I'm having a similar experience, so I hope it's okay to add to this thread. I'm using RO water and Kent RO Right because the tapwater here is so awful. I've adjusted the GH up to about 300 TDS using the Kent, and the KH to 6 using baking soda. I'm using pressurized CO2 into a canister filter intake and have been slowly turning it up to ever higher levels. But with a KH of 6 and a pH of 6.4 (AP test kits) I should have dead fish too. They seem fine, and they are goldfish which presumably want a higher pH. The plants are just now responding. WTF?

TW

 

[matpat]

Re: Question on Alkalinity and KH

I know what you mean TW. It seems if I keep my CO2 levels around 30-35ppm, I have no pearling and get green water very easily. Plant growth is pretty poor also. I have been experimenting over the last few months and slowly increasing my CO2 levels.

I've had a pH as low as 6.0 with a KH of 5.5. I didn't feel comfortable with the pH that low so I raised it up a bit. Something is a bit off either in my testing skills or my water...Probably my testing skills...

Maybe Tom can get me straightened out.

 

[rrguymon]

Re: Question on Alkalinity and KH

I would go with the bicarb alk only for the CO2 measurement.
That would give you the range of CO2 that seems appropriate 39ppm.

Regards,
Tom Barr

Thanks Tom I will do that. HAHAH the KH test kit was the only kit I was still using. Doing EI for a couple months conviced me I did not need the others. The KH kit is now pretty useless at least for my water. Oh well I guess I will save a few dollars on kits.

I have a ph controller and I will not use it now excpet as a monitor. I am just going on the bubble count and monitor the CO2. If the water company pulled a switch and I got full bicarb in the alk the controller would gas the fish for sure.

I would suggest that anyone else that suspects a simular problem check with their water utility for information on the alk and bicarb. I am pretty sure they have the information.

What research I have done agrees with Tom's assestment. The low bicarb component of alk is pretty rare and localized.

Thanks Rick

 

[rrguymon]

Re: Question on Alkalinity and KH

Ok today I was down to PH of 5.9 with a measured KH of 7.5 and still have happy fish and I still have a fuzz or hair algae growing and some BBA. The algae it is thriving and plants while growing are not really taking off.

I am injecting about 180 to 200 bubbles a minute into a internal reactor. That seems like it should be enough? The PH has droped from tap 7.9 to 5.9. Yet I still have all the symptoms of low CO2 and have not stressed the fish at all?

I am thinking about adding baking soda to my tank and putting in a Known level of KH and injecting CO2 to 30PPM based on that. Any other suggestions or cautions on doing that?


Rick

 

[Tom Barr]

Re: Question on Alkalinity and KH

Keep after cleaning the plants and pruning.
Adding Mg?
Since the fish are happy, stick with more CO2 ........slowly.
Giving it some time is the other thing.

Regards,
Tom Barr

 

[rrguymon]

Re: Question on Alkalinity and KH

I am not adding MG. I guess I can try that.

Rick

 

[Tom Barr]

Re: Question on Alkalinity and KH

See KH post in the general public archive
I think it will help you.

Regards,
Tom Barr