By Bob Goemans
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Dr Gs Marine Aquaculture 

Bob Goemans corresponds with John (L.A., CA)

John (L.A., CA) writes...

Dear Bob,

My question is as you know settling in wild caught saltwater fish requires a pH match to lessen stress. We use mono sodium phosphate to prepare matched water. I want to use carbon dioxide (CO2) to lower pH to 6.7 - 6.9 range and am wondering if this is going to work.

Is the low pH in shipping bags mainly due to carbonic acid/CO2 from respiration?



Los Angeles, California

Bob replies...

Hi John,

I’m not in favor of using CO2, even though usable, as it displaces dissolved oxygen, and besides, CO2 is very slow to equalize itself with the astrosphere.

Here are two thoughts;

If there are no fish in the holding/quarantine system, you can lower the pH in the system directly with sodium bisulphate, and the pH will return by itself to about 8.0 in about 24 hours from 6.8 or so, depending on existing buffering capacity. That’s pretty quick!


If it is a system with fish already in it but containing multiple aquariums, you can move all of the fish into some of the aquariums, clearing some to act as the receiving tanks. In those now acting as receiving tanks, shut off their supply of water from the main system. Lower their pH (either way), acclimate the new arrivals in those tanks, then slowly bring them back on line with a slow drip from the main water system. The slow drip from the return system will cause the pH to drift back to normal, and the excess water can overflow back to the main system, and providing filtration is good and the system is not too small in volume, should not affect anything detrimentally.

Furthermore, fish respiration is the major cause of the lower bag pH. Again, CO2 is usable, but sodium bisulphate is preferred, and keep in mind, haste makes waste!



Carbon Dioxide

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