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Old 18-07-2003, 10:16 AM
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Default CO2 toxicity question

I'm really struggling with my first ever DIY CO2 set up. My well water
is pH 7 and KH 8.
When I set up my tank last week, the masonry sand I topped the
substrate with must have released some carbonates because the KH went
up to 10. And my CO2 set up, with an airstone funneled via a
gravel-cleaning tube into my Eheim intake, must have been really
effective, because my pH dropped to 6.4. According to the chart I
have, that would be 130 ppm CO2. Could that be right? I hadn't put any
fish in yet, luckily. I reduced the CO2 (by chucking 3/5ths of the
mix) and did a 25% water change and my numbers dropped to KH 9 and pH
7. This was stable for a couple of days so I dared add some zebra
danios (not exactly delicate) and they are still thriving. The pH then
dropped to 6.8, which according to my chart meant a 45 ppm CO2
content. Supposedly fish can only tolerate about 20 ppm CO2. Is this
true? I don't understand how one could have a soft water tank and CO2
addition, since it would be so hard to stay above 20 ppm. Am I
missing some vital piece of info?

Meanwhile my plants are 'beading' like crazy. The crypts did some
melting, not surprisingly, but are stable now. I have 2x 55 watts on
12 hours.

I would like to get some algae eating fish--the algae is gaining on me
now--but it seems that otocinclus wouldn't take such hard water well.
Is this true? My tank is only 29 gallons and I dislike plecos . . .
any suggestions for me?

KMS in the mountains of California