Oxygen?
 

We have a 120 gal. tank using a Fluval FX5 filter, 30 gal. sump, Reef Octopus skimmer, aragacrete rock with live sand and Garf’s Grunge. The question is, do we have enough oxygen being let in to the water with the skimmer and sump? There is not an air bubbler installed in the system. The tank is now in the 8 day cycling period for the grunge and we do not have fish in there yet. Would like to make sure we are doing the right thing before we add any thing we can kill.

O2 is rarely a problem, you should be fine as far as that goes. High CO2 is a bigger issue in the winter because your house is all closed up. This will cause the pH to fall and it is difficult to get back up without fresh air in the skimmer. If you can run the air intake for the skimmer outside that would be ideal.

Sounds like everything is fine. One easy way to increase oxygenation is to be sure you have good surface movement in the main tank. point a powerhead or your return so that it causes the surface to boil slightly.

An air stone used full time will only cause salt creep later, and we all hate that.

Thank you! We have the tanks in a hanger for now so there is good air flow out side the tanks. As far as the surface movement we do have that so thats a good thing.

Yes, agreed. Keep an eye on ph, low ph can indicate excess co2.