uptake relationships between macros?

[cggorman]

Is there a predictable relationship between K uptake and either of the other macros? Potassium tests are scarce and expensive and I have a very difficult time doing weekly 50% PWCs.

I'm hoping that I can estimate potassium levels by testing for something else.

I know potassium is difficult to overdose and doesn't have any particular detrimental effect at fairly high concentrations, but with daily dosing using EI drops and only 10% PWCs, it seems likely my fert ratios aren't optimized and would lead to an eventual toxic overdose.

 

[Philosophos]

It depends on how much the plants are uptaking. You're going to max out at 7x EI levels (7 weeks for ~50% wc). Plants have thrived in these conditions; researchers have used 10x doses and higher. It is unnecessary though, and I'm sure the fish wouldn't enjoy it.

-Philosophos

 

[Tom Barr]

It might be useful to think about K+ in terms of pulsed dosing.
The vacuole can hold a lot of solutes, and nutrients, K+, and NO3 are some of the main ones.

If you pulse dose, say 2x a week, then it's not much of an issue.

How much the tank uses is really dependent on CO2/light.
So predicting a precise amount is not going to be easy.

With more WC, it is..........so that's the trade off.
Lamotte makes a K+ test kit for about 30-40$.
It will measure the higher ranges and prevent you from over doing it.

That's the cheapest option.

You can also a 10% weekly and then later, 1X a month or every other month, do a 50-80% WC. That would flush things out.




Regards,
Tom Barr

 

[cggorman]

Right. I understand all that, but if plants tend to deplete potassium and one or both other macro(s) at similar rates, it should be fairly easy to predict dangerous levels of K+ simply by testing for phosphate and/or nitrate. Assuming the relationship is there, if phos or nitrate are high, then I can assume potassium is also high and back down on all the macros at once. If the uptake rate varies significantly from one macro to the other, then I'll have to get a K+ test...and probably dose N, P, and K separately...


I guess I'm trying to with a sustainable dosing method rather than EI, so I can minimize PWCs on that tank. At the same time, I'm trying to avoid spending the $50 for the LaMott test if it isn't absolutely necessary with that type of dosing method.

(I already read and understand the test calibration instructions, but I still need to purchase the test kits.)

 

[Philosophos]

I'm not sure about any absolute ratios. Plants function strangely, and make use of different thing. Iron is infamous that way. I'd say the more of a macro it is, the more fun you'll have trying to figure it out. Things like nitrates come in NH4, NO2 and NO3 with the variables of fish food. Iron is satisfied between .2 and 6ppm+, PO4+ is altered by feedings quite nicely.

So while it's not a bad idea that K+ won't change with time, the rest may get messed around pretty well if you've got a decent population of fauna. Try the math for your self, in the past most of my conclusions have been pretty grim longer-term.

-Philosophos

 

[Tom Barr]

Right. I understand all that, but if plants tend to deplete potassium and one or both other macro(s) at similar rates, it should be fairly easy to predict dangerous levels of K+ simply by testing for phosphate and/or nitrate.

But that's simply not the case, many aquarist make this assumption and fiddle with the importance of "ratios" based on this poor assumption.

The issue is more about the Liebig's law of the minimum.
there is some interplay when something get really low, then the others are no longer taken up, but by and large, most are fair independent over a wide range.

It's only when moderate to strong limitations occur, that the others are downregulated.

I do not know what a dangerous K+ level is, I'd say in the 250ppm or higher range perhaps. So if you can be alright with 50-100ppm, a pretty large upper target you should not have any related issues for K+.

If you added 10ppm a week, then the max build up would be about 8-9X the weekly dosing, so 100ppm or so with 10% weekly WC's.

Realistically, that's pretty high and the actual value will be much lower.
You can also eye ball.

You need a test kit if you want more control and do not want to do a rare larger % water change, you are not going to get around it with some assumed rates, because they vary a great deal. There are a dozen or more factors that will alter that, so it's not a safe assumption to use.

Assuming the relationship is there, if phos or nitrate are high, then I can assume potassium is also high and back down on all the macros at once. If the uptake rate varies significantly from one macro to the other, then I'll have to get a K+ test...and probably dose N, P, and K separately...

I would.
Get a K+ test kit.

I guess I'm trying to with a sustainable dosing method rather than EI, so I can minimize PWCs on that tank. At the same time, I'm trying to avoid spending the $50 for the LaMott test if it isn't absolutely necessary with that type of dosing method.

(I already read and understand the test calibration instructions, but I still need to purchase the test kits.)

Well, why do any water change at all then?

Or rather, simply do a large say 50% once a month or once every 2 months?
Less work that 10% weekly.............

you can certain fanaggle a decent result with soem tweaking and go 1-2 month water change frequencies, particularly if you use lower light , say 1.5 w/gal of T5, that will go a long way to incorporating the idea of sustainable approaches, but still allow you to use CO2 and slightly faster rates of growth vs say Excel or pure non CO2.

You also have better stability with CO2, so less CO2 is needed and less fish stress, and much easier to dial in.

The lower light also reduces the overall rate of growth easier.

I did once a month water changes on a tank and it did great for 2 years like this, never touched a test kit, had nice plants and never any issues.

If you honestly want to use test kits, buy the good ones, they are well worth the cost for measurement.

Much like Gas tank CO2 vs DIY.......same type of thing.
Much easier to read and use.

Lamotte have also been much more consistent and accurate than the other brands for NO3 and K+. The PO4, try Hach. You are relying very heavily on test kits, so you need to use good ones, this is not bad advice and being cheapo there, but running high light is counter productive.
Put the effort and $ where is matters for your goals.

One assumption that should work okay, in regards to the above, 1:1 N:K ratios are likely going to be fine in most cases for most all plants. Note, this is not NO3: K+, ratios, you'll need to convert that to mass from atoms.

I'd focus on a sustainable approach holistically, not just with nutrients(Light, then CO2, then nutrient lastly, you also have a choice of WHERE they nutrients are, ADA AS or MS would be better alternatives since they do not enter the water column).

So add some MS if you are cheap, think about once a month or once every 1.5-2 months, run the light down to the lower ranges, dose lean, watch the plants, tweak CO2, top instead of uprooting plants, testing can go either way.

Should not require testing or much work and really will work well, use less light/energy/$/fewer water changes/easier CO2 etc, and easy dosing.
Folks often focus too much just on the nutrients/water changes.

Not enough on light/CO2/plant species choice.

So mull that over.

Regards,
Tom Barr

 

[cggorman]

I guess I'll pick up that K+ kit.

This is for a pretty low tech tank. DIY CO2, 1.5 WPG T12, Currently Flourite substrate, but I'm going to supplement by inserting some soil ice-cubes here before long.

For me, the test kits are more for trend tracking and disaster avoidance than fine-tuning.

My overall goal is slow and healthy plant growth, minimal cost and effort, and fish-friendly. This tank is in a location (bedroom, no sink) that makes it difficult to maintain with regard to water changes.

 

[Tom Barr]

If you use lower light like you said(1.5W), then the real disaster is that DIY CO2.
Dosing ought to be really easy.

I'd use about 1/3 EI and have a decent fish load and feeding.
You ought to get away with long time frames without water changes.

DIY CO2 is the Achilles heel there.

Why bother with testing or much dosing issues when you can do the MS for the sediment instead?

That will reduce if not remove the dosing(you can still dose, say 2x a week like the non CO2 routine in the articles/EI section).

Cost less than the test kit too.
More work initially, but over time, will do the goal much better.
Do some work now, to avoid longer term work on going........

That's what I'd do.
No test kits, no water changes, minimal dosing, little maintenance.

With gas tank CO2(spend your $ here, not on test kits, likely close to the same after it's all said and done), then there's very little work.
That's what I'd do given the choices you outlined.

Regards,
Tom Barr

 

[cggorman]

I'm actually a bit less than 1.5 WPG on that tank. Something closer to 1.3...

Sounds like what I'm going for. I'm sold.

Now I just need to figure out what MS means! Never mind... Found it. Mineralized Soil.

 

[Tom Barr]

MS=> cheap, takes moire work, DIY etc and time to make up, but cheaper than ADA AS.

I use a lot of it for my research.

Regards,
Tom Barr