By Bob Goemans
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Bob Goemans corresponds with Rob Hauck

Rob Hauck writes...

Hi Bob,

Been awhile since I've talked to you about my reefs, but all is now well with them.... (Thanks to your help over time). My question today concerns the use of ozone. My friend has a 2500 gallon fish-only tank. The open system consists of a large wet/dry, RK2 skimmer, and Delzone 4 eclipse ozonizer. The closed system consists of an Aqua Logic chiller and a prefilter canister and a carbon canister that holds approximately 25 pounds of carbon.

The tank appeared to finish cycling about 4 weeks ago, and then he began stocking fish at a slow rate. All tests on water quality have been great. At the end of this last week he noticed his ammonia and nitrite beginning to climb way up. Nevertheless, all livestock is doing great (No casualties). Now that I took up your time with that rambling on, I was wondering if the ozone running 24 hours a day, which is injected your favorite way through the skimmer, and then dropped directly back into the biological chamber of the wet/ dry, could be destroying some bacteria? The fish are all great and of course the tank is crystal clear of algae. Should the ozone be cut back on the amount of time it stays on or is 24 hours per a day fine?

Thanks again.

Rob Hauck


Bob replies...

Hi Rob,

Thanks for your email and glad to see all is well with your aquariums. As to your friend's large aquarium, I've always said that a protein skimmer should not be used during the establishment of the initial nitrification cycle, e.g., at least for the first couple of weeks. And in addition, certainly no ozone used during those first weeks, as both are reducing/inhibiting the spread of nitrifying bacteria that is so vital in establishing the nitrification cycle. Therefore, from what I can gather from your letter, the increase in ammonia and nitrite upon the introduction of livestock and feeding is to be expected, as the cycle has probably been impaired/not yet fully established. Furthermore, even though I recommend dispensing ozone through a skimmer, I do not recommend its effluent be passed over the biological media in the wet/dry, as some residual ozone is still active and that will kill off the bacteria living on the media/bio-balls. Instead, allow the skimmer effluent to pass over/through an activated carbon bed, and then back into the bulk water.

Immediately, I recommend correcting the skimmer effluent outflow as noted above, yet leaving the skimmer operating at this stage of development. And of course, would certainly not add any more livestock until the cycle is complete and there are no signs of ammonia and nitrite. And since this is a fish-only system, the use of ozone fulltime is acceptable, and I would think/hope it's an automated ozone system, and would set the ORP meter for about 380mV.

Hope this helps,




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