- I don't think such a low pH is good for fish (nor for nitrifying microbes)......................................... ....................Also, did you tried to use less N in your tank? I know it's hard to compare two states if you can't see it simultaneously. I mean, it's hard to compare your tank under (say) 10 ppm NO3 vs. 30 ppm NO3, and compare the growth rates of your plants. I understand that 30 ppm NO3 may results in fastest growth rates, but I think that with 10 or 15 ppm you would hardly notice any substantial difference. Also, this way you could check if adding NH4 makes any real difference.
I would love to be able to better control nitrifying bacteria, as they serve no useful function in my system. We know that plants uptake NH4, they can also uptake NO3 but must transform this form of nitrogen back to NH4 for use.
In a fish only system, or high pH system, it is these bacteria we know that help to support life through the transformation of highly toxic NH3, or excess NH4 into far less toxic NO3. Very useful function.
But now consider my low pH system that allows some amount of elevated NH4 concentration. I'm dosing 0.93 ppm of N as NH4 per day (1.2 ppm NH4) into what should otherwise be (without plant uptake and nitrogen transformation) an accumulated concentration of 6.2 ppm N (8 ppm NH4). Do I need this level of N (NH4) for reasonable plant growth? I should think not.
The issue is, that not all of the N as NH4 is available to the plants, some of it is transformed by nitrifying bacteria into NO3, which then must be denitrified by the plants back into NH4, requiring energy to do so. Without nitrifying bacteria, I would have no loss of NH4 to NO3, and hence, I could add significantly less NH4 to maintain the highly available (low energy requirement for use) form of N. Oh, and of course, with no NO3 dosing or nitrification of NH4 > NO3, NO3 concentration would be 0 ppm. Efficiency.
Some notes:......................................N has been lowered in an effort to keep NO3 levels within reason. My stem plants are really good N indicators. Lots of N (10ppm), nice big growth, little N, small growth. I'm trying to find that point where growth is nice and lush, and NO3 is low.
My N dosing has been as high as 2 ppm per day (NH4 + CH4N2O), and I can assure you that the affect on growth between that dosage and my current dosage (0.93 ppm N) is very noticeable, even without side by side comparison.
Here's the thing Marcel.......It wasn't the increased NO3 concentration that facilitated that increased growth of the stem plants. The NO3
being nothing more then a byproduct of an unwanted biological process
. It's the increased availability of more efficient forms of N that is the interesting part. I facilitate this availability by destroying some part of the nitrifying bacteria colony. Give or take, NO3 concentration remains the same as lower doses of N, through the process of water changes and destruction of nitrifying bacteria, but plant growth increases significantly.
So you look at my N dosing and see NO3. But I only supply NO3 data to show what the resulting NO3 concentration would be if all of the N sources were transformed to NO3. Perhaps I should just remove this data for increased intelligibility.
Since some part of the learning process in this system also means the reduction of manual tasks to support it, the constant removal of nitrifying bacteria goes against this standard. So I need to find that balancing act between available N, for my own personal needs and desires
regarding growth, and the concentration of an unwanted byproduct (NO3).
I understand that they may seem fine, but I don't think it's good for their long-term health/condition. In aquaculture and water chemistry literature you may find more relevant data that explain why it may not be a good idea to keep fish under such a low pH. But maybe the fish species you have are well adapted for it.
pH is simply an indicator, affected by numerous chemical species, and affecting numerous chemical species.
Is low pH the cause of long term health conditions because of
increased CO2, or
decreased alkalinity, or
increased concentrations of available heavy metals, or
decreased availability of other ions, or some combination
. These are the questions I would be asking Marcel, rather then painting everything with the same low pH is bad brush.
The ORP is quite complicated stuff.
Indeed it is. Home are some of my general opinions regarding ORP.
ORP and pH are tightly related. A pH drop of one equals an increase in ORP of 58mv. So my corrected ORP value against neutral pH is closer to 600mv (in other words, all other things being equal, my ORP reading should be 600mv if pH was increased to 7.0pH). Still somewhat high I guess, but probably not so high to generate the OMG YOUR ORP IS SO *UCKING HIGH responses that I have been getting.
ORP is a indicator of the oxidizing and reducing agents in the water. Looking at some of the reducing agents, we see, Ca, Mg, Na, K, Cl, Cu, Li, Al, and compounds containing the H- ion. Some of these I already have in excess of unpolluted waters (K+), others I just don't want at all (Li, Al), and others again that I would have in concentrations equal to some natural waters (Ca, Mg, Na, Cl, Cu).
I don't want to increase any of these elements, and I find hard to believe that low pH waters found naturally without significant pollution contain high levels of these elements. Instead, I believe that low pH waters in nature that contain lower ORP values are directly related to the level of oxygen consuming microbes. Since oxygen is an oxidizer, lower levels of oxygen will shift the ORP balance to lower mv values, and high levels of microbes are needed to clean these waters.
So then the questions remain. Are these microbes a valuable commodity to my system in the same quantities as found in naturally low pH waters? And regardless of whether I have the same concentration of these microbes vs water volume as these water bodies, it really only boils down to the oxygen concentration. Do I really want to increase the organic matter of my system to increase microbe concentration, to reduce oxygen levels, just to hit some possibly misguided interpretation of optimal ORP level?
If I add things like Citric acid (C6H8O7), pH lowers, and you guessed it, ORP increases.
edit: Correcting ORP against the pH of seawater brings my ORP reading to around 530mv. Still somewhat high, yes. But seawater contains significant amounts of reducing agents (Ca/Mg/Na/Cl).
PS: Are you sure your values are in ORPm, not ORPh?
The meter states it measures mv +/-. I can't say anything further then that.
- The alkalinity (KH) drop may be also due to the transformation (consumption) of HCO3 by plants. If they have not enough CO2, some of them may use HCO3 as their carbon source. If you are not adding CO2 gas into your tank, then probably you have just a "natural" level in your tank.
Highly unlikely. It is my understanding that plants will only begin to source C from HCO3 when CO2 concentration is significantly limited.
I absolutely have a natural level of CO2 in my tank. Natural levels of CO2 vary considerably.
I don't claim to have 30 + ppm of CO2, but I am very confident I have a CO2 concentration in excess of equilibrium with the atmosphere, which I might add, arguably more importantly then the concentration in itself (30 ppm vs 10ppm), is the fact that the concentration is very consistent.
edit: How confident am I that CO2 concentration in the water is above equilibrium with the atmosphere? Simple. I increase surface agitation and pH rises. If the water was in equilibrium, and increase in surface agitation would have no affect on pH.
In the following image I have marked the KH readings against pH.
(H+) + (HCO3) = H2CO3. The addition of H+ has increased the concentration of H2CO3 causing a reduction of HCO3 and pH. I suspect CO2 concentration has remained somewhat unchanged in this situation since the HCO3 concentration decreased relative to the increase in H2CO3 and is reflected by pH. Here, pH has dropped relative to decreasing HCO3 concentration.
If I want to increase CO2 production in this system, I'm pretty sure I need to have the same increase in H+, without the reduction in HCO3. In this situation the system would be generating excess C. Here, H2CO3 concentration would increase, HCO3 concentration would remain stable, but pH would change reflecting the increase in CO2, rather then the decrease in KH.
But, (H)CO3 only bonds with so many cations, and I have the desired concentrations of cations already in the water. I have some bending and warping of plant leaves that I'm pretty sure is related to Ca++/Mg++/K+ or some ratio of concentration between them. CaMg(CO3)2 is probably the best method of increasing KH, since I net two CO3 anions for every Ca and Mg cation, plus, CO3 is really good KH buffer being able to accept two H+ ions.
I think I will proceed by increasing KHCO3 dosing though, since this is very easy and I can accurately measure KHCO3 dosage. This will help to increase HCO3, plus increase K relative to Ca and Mg. I will note results on plant growth. If increased K doesn't fix the problem, I will then reduce KHCO3 dosing, and try an increase of CaMg(CO3)2 instead. In either case, hopefully one of the solutions will work, since increased HCO3 should also facilitate increased CO2.
Something I was pondering last night. When we inject CO2 into the water, some of this CO2 combines with free H2O molecules to form H2CO3. A decrease in free H2O molecules for an increase in Carbonic acid. Where we generate CO2 with the transformation of HCO3, we reduce HCO3 for an increase in CO2 and H2O. Which one do you think is the preferred method?
- Are you really sure your plants need 5 ppm PO4? Did you do any tests to verify this? I doubt they are able to uptake this amount, and even if they do, I doubt they really need it for growth.
Mainly because PO4 < 5 ppm = GSA.
But also because 1/20th Hoagland solution = 1.55 ppm P which equates to 4.75 ppm PO4.
Did you do any tests to verify this concentration of PO4 is detrimental? I have absolutely no concerns regarding this concentration of P. If this ratio of P vs other ions is satisfactory for a solution that is supposedly used by scientists world-wide, then who am I to argue. Mark my words though, while I am very comfortable with this concentration of P, when I am very comfortable with the concentrations of the other ions in my water, P will make the short list of ions to try and reduce to observe effects.
- Just a side note: It would be much better if you round the numbers in your table to one (or two) decimal places - at least for macroelements, as these decimal places you use right now are just a fiction anyway, and rounded numbers look more neat.
True. I'll have a look at figuring out how to make the spreadsheet automatically round off. Right now everything is automatically generated based on the calculated concentrations of ions against dosages.
The spreadsheet is here
if you're interested. But I've slowly been adding to it for some time, so it's a mess and probably not easy to understand.
Thanks for taking your time to respond.