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Discussion Starter · #1 · (Edited)
Hello, all.

I have had my 70Gal planted tank for a few years now, and it took about two of those to get the biomass equalized so that I wasn't getting pummeled with thread algae. My plants grow well enough that I have to "crop" them about every 5-6 weeks, cutting off about a third of their total growth. I use Excel (about two capfuls daily), Flourish (one capful a week), and Seachem Nitrogren (one capful a week) for the liquid ferts, and I drip CO2 from a 5lb tank at about 2-3 bubbles/second.

I normally keep about 15-20 fish going, most recently a couple of Parkinsoni rainbows, a couple of albino cory cats, about eight cardinal tetras, and a half dozen rasboras. Also, three swamp shrimp and six giant mystery snails (the orange ones) keep the glass clean, and about 3,000 tiny snails (hate those things).

Keep? Kept. This week I woke up to find my CO2 setup had dumped overnight, killing all of the fish, shrimp, and snails that I wanted to keep. The tiny pest snails somehow lived by floating at the top for a day. And I was just contemplating getting some additional fish next week; good thing I didn't. Huge loss for our family.

So I've removed all of the dead fish and snails, and I'm assuming what I couldn't find, the pest snails have taken care of. I didn't want anything to do with that tank for the entire week, after that. I just turned the CO2 completely off (the tank still has contents), and just dosed with Excel every day, no additions beyond that.

Today I decided to deal with the loss and figure out my next steps. I started reading, and found I probably should have done a water change right away, if for no other reason than to keep the bacterial colonies healthy.

I use two Fluval canister filters (a 304 and a 404) for backup filtration and for water movement (I'm a big fan of redundancy, coming from IT). The week prior to what I'm now calling "The Big Dump", I had just done a 30% change, as the nitrate levels were getting a bit high after not having done a change in about two months. I had cleaned half of the filter media in each canister, as I normally do.

Today I took all of the readings I would normally take before adding new stock; pH of 7.6-7.8 (normal for my hard well water, but the fish I usually add seem to adjust pretty well), almost no ammonia, almost no nitrites, but my nitrates were almost 40ppm. KH is about 170, again fairly normal.

I know I need to add a few fish at a time now, over the course of a month or two, to get the biofiltration slowly back to normal. However, I also know I need to get those nitrate levels back down to under 10ppm before adding new fish. The question I have is: is the high level of nitrates coming from a CO2-damaged bacterial colony, or from a lack of ammonia? I can do water changes over the next week, but I want to make sure I'm not causing more problems by doing so.

Thanks for any help!

PS: Forgot to add, my regulator setup was an Aquatek dual reg, which was always a tweaking POS, and half the time the relay wouldn't fire when the timer controlling the lights and CO2 turned off in the afternoon. The company was no help even when it was new; it had been in use for just over a year with no real issues, though. Today I decided to order a GLA setup; not taking any more chances. :\
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