I'm back to the conversation. Sick kids and my own tank issues the last two days have kept me really busy.
So it sounds like it's been narrowed to the depletion of the KH by something (bacteria or plants or both). I'm glad you tested the substrate too because I think that's what I'm dealing with in my tank but with pH rising. I will have to read up on the heterotrophic bacteria, what their biological process is and how that process effects the pH. What was posted above makes sense to me, regarding the faster reproduction of the bacteria equaling faster depletion of the KH. One question I still have though is the difference in the quarantine tank and the big tank. I think I asked before but I can't seem to find the answer? The quarantine tank appears to be fine but not the big tank? Is the substrate the same? Do you think there is the same bacteria bloom in the quarantine tank? Maybe not because the pH is staying constant and the KH is not changing. Are there plants in the quarantine tank? I just trying to think about a control in your situation and then the differences in the main tank.
As far as what to add to you tank. I would consider using both the Seachem Acid/Alkaine buffers and the crushed coral. The coral will help you slowly and steadily maintain your tank and the buffers will get you KH up there to start with. I would also consider using Seachem Replenish to increase you GH which is great for your fish. There are probably other products out there but these Seachem buffers do not contain any phosphates. Also if you have the pH you want, you use them both in together to keep the pH the same but increase the buffers. You will probably have to do some testing on a small scale with your water to determine how much you need of both achieve the desired results.
I appreciate you taking the time to do the test I suggested. Probably a better test would have been to increase the KH and the pH and dose with Flourish Excel before we did the photosynthesis test. But I think the bacteria seem a more the more likely faster KH remover than the plants. But I'm glad you did it anyway, even a negative test gives us information about the problem.
Can I ask about your pond pH test kit? Is it one test with a range of pH 5.0-9.0 or is it two tests like the master kit? My 1:1 well to RO water combination is reading 7.6 on the regular pH scale and 7.4 on the high range. So I'm assuming it somewhere in between but would love to have a test that measured 5.0-9.0 with one reagent. I might just order one anyway. I was thinking of a pH meter but then you have to have standards and calibrate it every time.
Also, I wanted to comment on the API test kits. So I went to my lfs Sunday and had them test my water. Our pH readings were identical but they said 0.25 ammonia, 0 nitrite and 0 nitrates. I KNOW there were nitrates in that sample because I had just finished my cycle. My readings were 0 ppm ammonia, 0 nitrites and 10-20 ppm nitrate. So I guess the point I was trying to make is I just don't know how reliable it is to compare results from difference test kits. The next time I go there, I'm going to bring a water sample AND my own test kit and ask to do them side by side.
So I have the exact opposite going on in my tank. I had a pH of 8 after my cycle completed and about 50% water change. I thought this pH increase was a result of adding the ammonia. LFS recommended 7.0-7.2 because that's what the fish I purchased were used to. I used the Seachem Acid buffer to lower it and it worked great but the next morning it was right back up there. So added some more buffer but it went back up again. I didn't think that was supposed to happen with the buffer or so I thought. And now I was chasing pH which is bad and not at all what I wanted to be doing. So I figured something in my tank was making it go up. Did a 50% water change, added a little bit of peat, removed some rocks, next day pH is up, next day (today) pH is up to 8.2! The rocks were my first guess but I did do the vinegar test on all before soaking and adding to the thank. Most of the rocks are out now, did the vinegar test on all of them again. No bubbling. So that leaves the substrate. I used Flora-max and a little bit of Eco-complete. I did some reading before buying it and it got great reviews, didn't read anything about a pH issue, didn't know to specifically search for that. Now I have and I have found many threads with people testing it and seeing a pH increase. So I set my own test up this morning. I have 6 pints jars, 2 that have eco-complete from a new bag, 2 that have Flora-max/eco complete mix from the tank, 2 have nothing. Three jars have 1:1 Well:RO water and three jars have RO water. All substrate and water weighted out to be exact in all cases and water temperature adjusted to the same within 0.5 degrees F. The temp will decrease over time because there are no heaters in the jars. But they started the same and will adjust the same with room temperature. Also I capped all 6 jars to keep that variable constant. The starting pH on my 1:1 mix was 7.4 and the starting pH on the RO water was 6.8-7.0 (hard to tell the difference between) So I'll let you know how this goes and if it might have any relation to your own tank problems. Maybe we should just mix our tanks 1:1 and we'd both have something that works!
So I have added some photos. I took some photos of what my GH and KH tests look like with tank water and Distilled water so you could see. Also uploaded a picture of the substrate test I set up this morning. So very very glad I listened to the lfs and held off on the dwarf gouramis and the cherry shrimp now that I'm also dealing with tank issues. My fish seem fine though. I have stopped trying to adjust pH with buffer. I have added more peat though to hopefully keep the pH from drifting higher.
With all that's gone on with my own tank, I can certainly understand why beginners give up. This has been way way more than I ever anticipated but I am committed. However, I would still love to see the #1 beginner article be about water.
Does anyone have any suggestions on what I should be looking at for substrate if it turns out the Flora-max/Eco-complete increase the pH of my water? I'm just aiming for a low tech tank with easy growing plants. I currently have 1 large mother amazon sword with several runners and babies, 3 java ferns, 2 moss balls, some micro swords, 2 anubias hastifolia, 4 banana plants, 3dwarf sagittaria. Everything has new growth except the java ferns and moss balls but they both look great. I have a 29 gallon tank with a Finnex Stingray lamp that I'm running from 7-11:30 and 4-9 daily.
I hope we can both figure out our tank issues and move one to happy fish owners!