I first set up my tank on June 21 and ran the filter for almost a week (tank only had blasting sand and water in it). I added fish on June 27, along with TSS. On July 2, I tested the water, and my pH was 7.8. On July 4, it was still 7.8. But then the next day, July 5, it was 6.8. On July 6, it was 6.8 again. July 7 and 8 it was 6.4. And finally, both yesterday and today it was 6.0. Now I know that we should generally just leave our pH alone and that most fish will adapt to whatever pH your water is. However, I'm concerned with the large drop. From what I understand, drops in pH are more harmful to fish, and if the water I put in is 7.8 and then it keeps dropping to 6.0, isn't that a not-so-good thing? This happened in the past as well. When I first started keeping fish 2 years ago in April 2013, my pH was 7.8 for months and months. Then suddenly it started dropping to 6.0 in my tanks (I had 4-5 tanks running). I haven't had fish for the past year and some months, so I don't know what my pH would have been last year. I know I tested the hardness way back when, and it wasn't very high. On Monday I put in a cuttlebone in the hopes that raising my hardness will buffer the pH, but as you can see above, my pH just kept dropping. I'm also concerned about establishing/maintaining a cycle with a pH of 6.0. This evening, I tested the pH and hardness of my tank water and the pH and hardness of my tap water. Here are the results: Tap: ph - 7.8 GH - 3-4 KH - 4 Tank: ph - 6.0 GH - 5-6 KH - 2 I tested the KH in both water twice and got the same results. What do you make of this? Should I attempt to harden my water in order to maintain the 7.8 pH when I add the tap water during water changes? I would prefer not to deal with chemically altering things, but I do have the cuttlebone in there (which didn't seem to work?) and today I bought a bag of crushed coral. I could put some in a bio bag and put in one of my filter media baskets. But I wanted to lay out the situation here first. My parameters right now are: Temp: 79 pH: 6 Ammonia/Nitrite/Nitrate: 0 It's been that way since Sunday. Previously I had Nitrate readings of 5 on July 2 and 10 on July 4 (0 ammonia and nitrite both times) but then Sunday I noticed my barbs gasping at the surface. I tested and had 5+ nitrite. Did 2 50% water changes, and it was down to 0 by Monday morning. I've had the same results every day since then, except for the pH dropping over the course of the week. So I had thought the TSS was starting to work but then with the high nitrite spike and the large water changes, I think I killed the cycle. I've started dosing the tank with Stability per bottle instructions. On day 2 of that. Fish in the tank are: 1 pearl gourami 7 Cherry barbs 6 sterbai corys Tank is 36g non-planted with Black Diamond blasting sand for a substrate. I have a Fluval 406 canister filter running.