Re: Potassium Bicarbonate and Potassium Phosphate = overdosi
Nat N said:
I have read some opinions – like this:
Quote:
<<<The nitrifying bacteria which oxidise ammonia in to nitrate use 4.8 grams of oxygen is used, 7.14 grams of calcium carbonate (or other carbonates) for every gram of ammonia converted in to nitrate.
The oxygen replenishes itself at the water surface but the carbonates have to be replenished by either water changes or by adding buffers to the water. It is the carbonates which hold the pH stable, so as the carbonates become depleted the pH will begin to fall. If you get to a point where the carbonates are completely depleted the pH will crash and biological filtration will stop.>>>
Unquote.
I suppose, this is not relevant/true for planted aquariums for many reason (production of oxygen by plants and a much smaller contribution of bacteria into the general balance e.g. uptake of ammonia by plants, etc. etc...)
This is from another forum – you see why I keep on getting all confused? To be honest, I am not sure I need to buffer the KH in my tanks any more – the Potassium will be added by dosing Potassium Phosphate anyway..
Well, there are so many processes going on that, as you mentioned, effects of some processes cancel the effects of others.
Here is a typical 1st stage aerobic bacterial nitrification equation:
(NH4+) + 1.5(O2) ----> (NO2-) + 2(H+) + (H2O)
The 2nd stage looks something like this:
(NO2-) + 0.5(O2) -----> (NO3-)
Now, really, lets forget about calcium carbonate for a second, because it's clear from these equations that because these are aerobic, a lot of Oxygen is being used to convert Ammonia to Nitrate. Lack of Oxygen kills a lot of fish in tanks so if there was a pH crash (which we know is unlikely) and if these bacteria decided to stop nitrification due to low pH, the plants will absorb the ammonia, and will do so without adversely affecting the Oxygen levels. Isn't this a good thing? Who cares if pH drops and Nitrosomas /Nitrobacter decide to take a vacation as a result? In any case, a pH of 6 does not mean that these microbes stop functioning. It just means that they don't nitrify as much as if the pH were at 8.0. Also, ammonia is less toxic as the pH falls because it converts to a higher ratio of NH4+ - so lowering the pH does more good things than bad things. I don't really see a problem here. Higher Oxygen due to direct plant uptake of ammonia/ammonium (plus extra Oxygen expulsion from photosynthesis), better plant health, lower toxicity of any ammonia/ammonium that is not immediately taken by the plants. I can't see why this is even an issue.
Nat N said:
Walstad highlights an example of somebody trying to combat Phosphates in their tank by adding FECl3. They reported what they thought was signs of Phosphate deficiency which she promptly dismissed as Iron toxicity in plants. According to her, such thing as toxic destructive levels of Iron can happen... (page 13 of her book). She also states that chlorosis and Iron deficiency in plants can be caused by excess of Copper, Manganese and Zinc (the same page). She does, however, state that PH between 6 and 8 is “safe” in respect of metal toxicity...
Well, as I mentioned in an earlier post, I've doses massive amounts of metal micronutrients in my tanks and I have never seen metal toxicity in plants at any pH - and I'm generally considered to be an extremist as regards dosing. I probably dose higher quantities of nutrients than anyone else in the known world (or at least I'm in the top 10, I reckon). I can't recall who it was, but I was embroiled in a bitter argument with one of those lean dosing acolytes, and they referred to me as "The High Priest of Nutrient/CO2" because I kept telling people to "add more", "add more" of everything.
Here is a tank dosed with 3-4X the EI suggested macronutrient levels, 6X the EI micronutrient levels (3ppm Fe) and enough CO2 to drive the tank water down to a pH of around 5 (although, this is not quite the same as your conditions because the KH and GH were high). I did this specifically to test the theory of low pH and nutrient toxicity. I failed to induce any form of toxicity in any plant doing this. It is possible that the toxicity issues arise if the plant is in an emmersed state and not submersed. There is no "practical" limit to the amounts of metal micronutrient you can add or practical lower limit to the pH in which you can grow excellent plants in. What's more important is that you feed ample levels of nutrients, have excellent CO2 without damaging your fish, have good flow energy, to distribute that flow properly, to not go crazy with lighting and to keep the tank spotlessly clean via frequent and massive water changes. These are enough things to worry about, believe me. You don't need to worry about all that other stuff. It's all good to know, but ultimately it's irrelevant. The more you worry about things that don't matter, the more trouble you'll have.
Here I lowered the CO2 injection to allow more fish. This caused the pH to rise to a minimum daytime level of about 6. But remember that it isn't the fact that the ph rose that allows the fish thrive, it's the fact that the CO2 toxicity level was reduced. The net effect was a rise in the pH. So this highlights the second and perhaps more important point that when we measure the waters pH it's necessary to understand WHY the pH is at it's value. It's the thing in the water that
causes the pH to rise or fall that is important, not the actual pH value itself. I think that's what people completely disregard when analyzing these parameters. It's this poor analysis that often renders the parameters useless.
Nat N said:
By the way, Gmartins report on the PH fluctuating from 6 to 6.8 – is it not quite a lot of difference? Some people use solenoids to switch the CO2 supply off at dark time. I have not got one yet but probably it is a good idea – economy and plus more stable CO2 level?
Yes, you are absolutely right. This is a humongous difference. It's a 6X increase in acidity and I'd even go as far as to say that Gmartins would do even better to have pH fluctuation of at least 10X instead of 6X. Neither his fish nor his plants care about this and that's what we are trying to get through to people - to forget about pH stability because you will not see any practical benefits to maintaining a stable pH. This adds no value whatsoever unless you are breeding fish.
Cheers,