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"Are my CO2 levels dangerous yet?" and other questions


This past Saturday (9/25) I modified the output diffuser on my Magnum 350 to
minimize CO2 effluxion (? or whatever it's called when it escapes from the
water). Apparently the modification was effective, because CO2 levels went
from a previous range of between 15 to 25 mg/L to somewhere between 45 and
57 mg/L this morning. I noticed it had reached 40 mg/L on Sunday morning, so
I slowed my bubble rate from 60/min to 50/min. Obviously that was not
enough, so I've lowered it to 30/min.

My immediate concern is whether my fish and shrimp are in eminent danger,
since I've read various maximum thresholds such as 30 mg or 40 mg. I know
mine is too high, but currently there are no signs of any distress that I
can see, and all fish and shrimp are actively eating, swimming, etc. Since
the plants will lower the level during today while the lights are on, I
don't want to take emergency expulsion measures and change the pH rapidly
unless it is merited. Has anyone experienced fish distress at this level of
CO2? At what threshold have others actually observed symptoms of CO2
overdosing in fish?

Secondary to this, the reason I stated that the CO2 levels are between 45
and 57 mg/L is because I can't tell exactly whether my pH is closer to 6.5
or 6.6 (with a kH of 6), or even some other level, due to the fact that the
color chart in my test kit doesn't exactly match the solution color (at
least to my eyes). I'm using an Aquarium Pharmaceuticals kit with a range of
6.0-7.6. Can someone recommend a kit with either a narrower range and/or
finer resolution (and easier to read)?

Also, when people refer to bubble rate, is there a "standard" size of
bubble? I know this is a relative factor, but does anyone know what size
tubing or opening will produce a given size of bubble, or does this depend
on hardness of the water and/or other factors?

Please feel free to cc me directly if you think I may have an emergency
situation here. :D

Thanks in advance,

Dan Dixon