Fishless cycling - Help! pH dropped to 6 or lower

[iankim_sf]

I have a 20-gallon aquarium and I'm about 3 weeks into fishless cycling. I am using the API water testing kit to monitor pH, ammonia, nitrite, and nitrate levels.

PROBLEM:
I just tested the pH, and since a week ago the pH has dropped from around 7 to 6 (or it could be lower, but the kit doesn't measure below 6).

I'm worried because I read that low pH will interrupt the nitrification cycle by stalling out the bacteria. I've also read, of course, that trying to change the pH is challenging and it can be a problem to try to overcome the buffering system in the water.

What should I do?

I'M IN THE "NITRITE" STAGE OF THE CYCLE:
In the last several days, the nitrite level finally came up (currently off the charts). I have trace amounts of nitrate, and I can definitely see that ammonia is being digested. The ammonia level dropped significantly a few days ago, so I'm now adding a couple mL of household ammonia every other day to keep the ammonia level up around 2-3ppm. (ZForce ammonia, no scent, additives or surfactants)

WHAT'S IN THE TANK:
I'm using ADA AquaSoil which released a fair amount of ammonia into the water for the first couple of weeks. I have a few pieces of driftwood and a half dozen sword plants, all purchased from local pet stores.

The plants are starting to turn brown, so it's possible that plant decay is acidifying the water. Should I take the plants out?

 

[jlk]

Hi! Welcome to AA!!! It sounds like your on the right track but you are correct that a ph crash may stall your cycle. It can be easily addressed with a large water (80+%) change to restore your buffer levels and bring the the ph back up to more normal range. This will also reduce your nitrite levels which can stall your cycle as well when they are in excess. If you find your ph dropping on a regular basis, then an additional buffer such as crushed coral or aragonite may be necessary to stabilize your kh and ph levels. Please ask if you have any questions!

 

[iankim_sf]

Thanks so much, jlk.

Any thoughts on what might be causing the pH crash? I will try the large water change, but worried that this won't solve the root problem.

Thanks again,
Ian.

 

[jlk]

Thanks so much, jlk.

Any thoughts on what might be causing the pH crash? I will try the large water change, but worried that this won't solve the root problem.

Thanks again,
Ian.

It's fairly normal in a fishless cycle. Carbonates in the water keep your ph stable. Your good bacteria use them to process ammonia. Your adding alot of ammonia. As they get depleted, the ph becomes unstable and starts to fall. A water change will restore buffers (carbonates, generally) and minerals and stabilize the ph. You will need to keep a close eye on the ph though- if ph crashes become frequent, then more may be needed to stabilize the ph until your cycle is complete and stable.

 

[CharlieKlein]

I'd strongly reccommend crushed coral in addition to a water change. My tank was fishless cycling for 3 and a half weeks, and right before I was finished ph fell to 6 And now my tank has been up for nearly 2 months and still no fish.