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Old 25-07-2004, 01:06 AM
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Default how much co2 is too much

"Joe" wrote in message ...
I've seen in some places that CO2 levels above about 15-20ppm can be harmful
to fish but I've also seen that you can go much higher without harming fish
as long as the O2 content is adequate. I'm asking because I have liquid
rock coming out of the tap, the KH is 15 degrees. I use a pH controller and
I have it set for 7.5. I am getting ready to start stocking with fish and I
want to be adding tetras and corys and other fish that prefer low pH. How
high can I bring the CO2 without it being a problem for the fish?

Up near this range you need good precise pH measurements.
You'd be a tad low at 15KH, nothing wrong with that type of water
though. It's still a CO2 issue, not a hardness issue for the plants.
7.2 would be a good target pH for a KH of 15.
That will give you 28ppm and with error added in for both KH and pH,
that will be + or - about 4-5ppm.

Plants do not need any more than 30ppm at any light level.
This is based off max CO2 levels and max light levels with fast
growing stem plants done by Bowes here at UF.

This is also what I found to work well when I used high light in the
At low light you still get good effects........even better because the
plants are able to adapt well to lower light and still get the
benefits of a non limited CO2 supply.

I have kept cories, even bred them, cardinals, Rummy noses, etc in
hard water. Altums, Apistos and Discus you will want to use RO and
blend to reduce the hardness down to 3-5 for KH/GH.

This is a fishg issue then, not a plant issue.
These fish have done excellent at 20-30ppm of CO2 and some slight
surface movement. Surface skimming also helps keep the levels higher
without O2 depeletion which is why the folks that believe more than
15-20ppm is harmful.

Either that or poor testing kits for KH/pH measurements etc.
Gasping fish is typically poor O2, not CO2 as many assume.
A well run fully planted tank does not have problem at 20-30ppm CO2.
My Discus would have never spawned if they were in trouble from my
high levels of CO2.

Tom Barr