I have a 10 gallon planted tank currently in the process of a fishless cycle. Yesterday I was doing my usual water tests and everything appears to have flatlined. My pH was as low as my API kit could measure; no ammonia, no nitrite or nitrate.
After doing about a 25% water change last night and dosing ammonia to around 1.0, my pH spiked up to around 8.2 but has gradually fallen back down to 6.0 on the test kit as of around 1 pm today, while my ammonia is mostly the same.
My tap water has a base pH of 7.2, before and after dechlorinating with Prime.
My tank had started to cycle recently (I'm using Seachem Stability and Seachem Pristine) and I was finally starting to see the conversion of ammonia into nitrite into nitrate, but I'm afraid this pH business has ruined my beneficial bacteria growth or at least made it fall dormant.
I use a modified Aqueon quietflow filter with sponges, 2 bags of ceramic rings & a packet of Purigen wrapped in sheer panty house. No activated carbon. I've read that Purigen can crash your pH after "regenerating" it in bleach, but mine is still relatively new and I haven't needed to do that yet. It was cycling with the purigen in it just fine before. I also use a bubble bar at the back of the tank, and I'm kind of a newb so I have no idea if oxygenating the water continuously affects pH or not. There is a piece of driftwood in the tank as well, but its aged and doesn't leech tanins. I also dose with Excel and ferts a few times a week, although admittedly I've been struggling with the exact dosage for a 10 gallon aquarium. I don't know if overdosing Excel would cause the pH to crash or not.
The only change I've made recently was replacing my terrible Aqueon light with a Finnex 24/7 planted+ cc series light. I've read that during peak photosynthesis plants can affect the pH reading. Is this true? Are my plants actually dropping the pH or is it a superficial reading, and if so will it return to normal in the evening? Is this dangerous to livestock? Can Excel affect the pH? If it's not the plants, what am I doing wrong? Please help!