Carbon dioxide toxicity


Carbon dioxide level >60 ppm
Normal CO2 level is exceeded.
Dissolved oxygen low < 6mg\L
Most aquatic fish in freshwater or seawater require oxygen levels above 6mg/L. Check oxygen level.
pH water low <6.5
A few species of freshwater fish (Discus) can tolerate lower than 6.5 pH.  If lower than this and problems, suspect this a possible cause.
Sits on bottom
Fish sits still in upright position, on the bottom of tank or pond.
Laying on side
Fish lies on side, usually motionless.
Respiration slow
Fish's breathing is obviously slower than normal.
Listless and lethargic
Fish moves very lazily in water, much less than normal, lacks interest.
pH Water normal 7.00
It is possible for CO2 toxicity, even with normal pH level .


CO2 level too high, Carbonates and Bicarbonates too low.


Check levels of CO2 and Carbonate levels with test kits. Problem can be remedied easily if cause is determined within a few hours.


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The level  of CO2 in both fish farms and aquaria can easily be kept to safe levels by use of a CO2 controller.  


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