Low Ph And High Nitrites

VAS729

HI everyone. I've been lurking for a few weeks reading up on all I need to learn to start a freshwater tank and have recently begun starting to cycle. I'm setting up a 30 gallon tank as my main tank and a 10 gallon tank as my quarantine/eventual hospital tank and I'm cycling both from scratch using Prime and Stability.

The 10 gallon tank started cycling about 10 days ago. I'm using liquid ammonium chloride (Dr. Tim's) and dosing to 4 ppm ammonia (all testing is with the API Master Kit).

After about a week, I was going from 4 ppm ammonia to about 1 ppm ammonia in about 24 hours, redosing to 4ppm ammonia each time. As of a few days ago, nitrites were off the chart (>5ppm) and nitrates were around 10ppm. So I thought I was almost home free. However I haven't had any change in nitrites or nitrates since then (about 4 days) despite regularly adding ammonia. I tested pH yesterday and it was down to <6.0 (so I tested KH and it was also off the charts low, essentially the first drop was yellow in the tube). I did a 90% water change and added a little sodium bicarbonate to the tank and dosed ammonia to 4ppm. After the water change, nitrites were down to 0.25ppm and nitrates were down somewhere between 0 and 5ppm. This morning (12 hours later), I took my water parameters. They are pH 7.0, ammonia 1.0ppm, nitrites >5.0ppm, nitrates 5ppm.

I just want to check in to make sure I have a grasp of what's going on here. From best I can tell, because my water is already low on KH (around 2-3 dKH out of the tap), the carbonates in my tank were quickly depleted by the cycle, causing the pH to drop. I have read (with mixed opinions) that the bacteria that convert nitrites to nitrates are more sensitive to low pH than the ones that convert ammonia to nitrites. This would be consistent with the numbers I'm getting I guess. As the nitrite-oxidizing bacteria struggle at the lower pH, the nitrites accumulate to off the chart levels as the ammonia oxidizing bacteria continue to do their job to convert ammonia to nitrites. Does this sound right?

So I guess after that long-winded history, is my best bet to continue with large daily water changes and treatment with sodium bicarbonate to keep nitrites down and pH up? And hopefully the nitrite oxidizing bacteria will recover and start converting the nitrites to nitrates, and I'll be home free? Any other suggestions?

Part two of my question: my 30 gallon tank is a little behind the 10 gallon because it got setup a little later. Currently I'm converting 4ppm ammonia to 1ppm in about 12 hours (as of this morning). But now nitrites have reached >5ppm, and nitrates are ~10ppm. pH in the 30 gallon tank is still around 7.2 so I think the nitrite oxidizing bacteria have a better shot here. What should my step forward be here? just keep dosing ammonia and monitoring pH? Or should I expect the pH to drop here also like it did in the 10 gallon tank? Any recommendations appreciated.

Thanks so much all!
 

AquaticJ

Minnowette can help, I don't have time right now
 

Inactive User

Does this sound right?

Correct. Carbonates are gradually depleted by two reasons: (1) the increasing acidification of the tank water by the oxidation of ammonia to nitrate; and (2) nitrifying bacteria utilise carbonates as a substrate for carbon.

Generally the effect isn't particularly prominent over the short-term, but in cases of soft water (in your case) and exponential bacteria growth (again, in your case), KH tends to rapidly decline.

I think your nitrite accumulation is a reflection of both (1) low pH; and (2) the typical nitrite spike that occurs in cycles as NOBs has a reproduction rate of some 13 hours (compared to 7 hours for AOBs). I find that the inhibitory effects of pH are quite similar for both AOBs and NOBs (optimal range: 7.5 - 8.5; dormancy at 6.0). I think it's much more the case of interspecies variation in pH resistance than any particular differentiation between AOBs and NOBs. See the "long answer" under heading (5) of this thread for a more comprehensive discussion of why pH affects nitrifying bacteria (the precise mechanism of action is disputed).

I would recommend dosing 2 ppm ammonia instead of 4 ppm: there's little evidence to suggest that ammonia excretion rates in household aquariums reach anywhere near 4 ppm per day ammonia. Most resources recommend 2 ppm as a happy balance.

But continue to add sodium bicarbonate whenever pH drops precipitously. I would recommend doing this for your second tank as well. As for whether pH will drop: it should. But we've learnt that tanks from the same owner using the same water and the same products will often show a lot of variation in how the cycle progresses.
 

VAS729

Correct. Carbonates are gradually depleted by two reasons: (1) the increasing acidification of the tank water by the oxidation of ammonia to nitrate; and (2) nitrifying bacteria utilise carbonates as a substrate for carbon.

Generally the effect isn't particularly prominent over the short-term, but in cases of soft water (in your case) and exponential bacteria growth (again, in your case), KH tends to rapidly decline.

I think your nitrite accumulation is a reflection of both (1) low pH; and (2) the typical nitrite spike that occurs in cycles as NOBs has a reproduction rate of some 13 hours (compared to 7 hours for AOBs). I find that the inhibitory effects of pH are quite similar for both AOBs and NOBs (optimal range: 7.5 - 8.5; dormancy at 6.0). I think it's much more the case of interspecies variation in pH resistance than any particular differentiation between AOBs and NOBs. See the "long answer" under heading (5) of this thread for a more comprehensive discussion of why pH affects nitrifying bacteria (the precise mechanism of action is disputed).

I would recommend dosing 2 ppm ammonia instead of 4 ppm: there's little evidence to suggest that ammonia excretion rates in household aquariums reach anywhere near 4 ppm per day ammonia. Most resources recommend 2 ppm as a happy balance.

But continue to add sodium bicarbonate whenever pH drops precipitously. I would recommend doing this for your second tank as well. As for whether pH will drop: it should. But we've learnt that tanks from the same owner using the same water and the same products will often show a lot of variation in how the cycle progresses.

Thanks so much. Added more bicarbonate to the small tank (as pH had dropped again) and dosed ammonia to 2ppm (nitrites maybe a little lower but still at or close to 5...honestly I find the colors in the kit very hard to differentiate). Nitrates have risen to 20-40ppm.

Appreciate your advice. It’s comforting to hear that (at least the gist) of what I’ve gathered from my reading online led me to the right conclusion.
 

Inactive User

I share the same issues with the nitrite test: I can't tell a lick of difference between any colour from 2 to 5 ppm.

Try diluting a sample of tank water with 50 to 95% tap water (or bottled water if your tap has trace nitrite). Usually the highest solutions are the more useful as the lower range colours are more obviously apparent. For e.g. it took a 95% dilution with tap water for me to determine that my tank had 10 ppm nitrite.
 

VAS729

I share the same issues with the nitrite test: I can't tell a lick of difference between any colour from 2 to 5 ppm.

Try diluting a sample of tank water with 50 to 95% tap water (or bottled water if your tap has trace nitrite). Usually the highest solutions are the more useful as the lower range colours are more obviously apparent. For e.g. it took a 95% dilution with tap water for me to determine that my tank had 10 ppm nitrite.

Thanks. I figured I could do this, just never actually went for it. The scientist it me just screams every time I use the kit...I just want a nice numerical read-out from a nice reliable instrument. None of this color matching! When I test tomorrow, I’ll do a dilution.
 

VAS729

I continue to be mystified by my tanks. The 10 gallon is going through HUGE pH swings: I treat with sodium bicarb and the pH comes up, but within 12-24 hours, we're back down below pH 6. Currently it's processing 2ppm ammonia to nearly 0ppm within about 12 hours. I did a dilution last night to figure out my nitrites were around 50ppm. I did a large water change so that I could try to better track my nitrite consumption rate.

On the other hand, the 30 gallon tank is seemingly happy, with the pH stable between 7.0 and 7.2, also processing 2ppm ammonia in 12 hours, just waiting for the NOB to catch up and process nitrite. A bit irritating that my main tank seems like it will be cycled before my quarantine tank. Not sure what's making the difference. I guess all is not equal in the tanks...the 30 gallon is planted so there's substrate and plants. The filter setup is also different. The 10 gallon is a bare tank, so I guess that contributes.

My main remaining question is: should I be worried that my pH will never be stable in this tank? Or do you think that once the cycling blues are over, the pH will stabilize?
 

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