fishless cycling and pH is dropping like crazy

[NBCGLX]

Started to cycle the tank the weekend after Christmas. All was chugging along fine and then pH started dropping, very slowly at first. I know that pH fluctuates quite a bit during tank cycling, so I didn't think anything of it. Then, last week, just as nitrite levels were starting to drop, pH started dropping significantly. I'm talking started at 7.6 and was down to 6.4 in a matter of a day or two. I did a 50% water change to try and get the pH back up, and it helped a bit (brought it back up to 7.2 or so). Within another day or so, pH was down again in the 6.2-6.6 range so I did another water change, this time a large one, doing about 70%. The pH returned to about 7.4 but now, only a day or so later, the pH is down to 6.2 and I'm going to assume that it will continue trending downward. The other strange thing is that whereas ammonia was dropping from 4 ppm to 0 in about 8 hours, it's now only down to 1 ppm after about 12 hours. This tells me the cycle is stalling, and I'm thinking it's due to the significant pH drop as I know that if pH gets too low for too long the ammonia conversion process can change (ammonium rings a bell).

What to do?? It's clear to me that water changes aren't helping (tap pH is right at 7.6). I tried to add a pH buffer (only affects pH; doesn't have any other properties according to the box) but that didn't seem to help at all. Should I lay off the ammonia dosing for a few days to see if pH bounces back, keeping ammonia down to 1 ppm or so, so as not to kill off the bacteria colony?

 

[Mebbid]

Test the ph of your tap water after it sits out for 24 hours. This will tell you if it's the cycle or your water.

If its the water, then you can try a handfull of crushed coral in a filter media bag. It will increase the dkh buffering the water.

If its the cycle, just do water changes or you can look into adding baking soda. I'm not sure of the amounts off the top of my head, you will have to do some digging.

 

[ScotJudd]

I use bicarbonate of soda at the rate of 2.5 ml per 10 litres of tap water to raise Kh from near zero to Kh 6.
Ph sits at about 7 despite having Co2 injection which tends to acidify water.
Any higher than Kh 6 and my tank Ph starts to rise. At Kh 6 it doesn't drop below Ph 6.8.
It's worth testing the Kh of your tap water.


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[NBCGLX]

I tested my tap water pH after letting it sit for 24 hours and it tested right around 7.4. Seems it's the cycle causing the pH to drop, which isn't unheard of. Water changes weren't helping to buffer it and prevent it from continuing to drop, so I picked up some Sachem alkaline and acid buffers and targeted a 7.0 pH. Within 24 hours pH is holding steady at 7.0 and my nitrites have started to come down. I think we're back on track!

 

[ScotJudd]

Sounds like your tap water is very soft and needed buffers. Glad you're back on track.


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[NBCGLX]

The pH has been holding steady at 7.0 and in the last couple days nitrite levels have started to come down. I tested the water this morning, and though ammonia hadn't fully come down overnight (testing at .25 ppm), nitrites were gone. Curiously, nitrates still aren't showing at all...and I've been very careful with the test, following the directions to a 'T'. Also curious, is that pH has dropped overnight again, down to 6.4 (it was still 7.0 when I tested last night). I added more Seachem to further buffer the water and bring pH back up. I can't get my head around these strange pH fluctuations!