Well nitrosomas and nitrobacter need dissolved oxygen. I suppose putting your air bubbles near the filter intake would help break up the bubbles and increase the rate that oxygen is dissolved into the water. I don't know what the long term effects are on your FX5 or its pump. The FX5 is a $200 piece of equipment and most of us who use one aren't feeding air bubbles into the intake. Our bio media is working well enough to keep ammonia and nitrite at 0 without feeding it air bubbles. Because that is the case, I wouldn't recommend doing it. My thought is why bother and take the risk of messing up an expensive piece of gear when we know feeding it air directly isn't necessary to achieve 0/0?
Once you get your turtle in the tank, you'll start getting a little phosphates in the water which is what you want. The nitrifying bacteria will also consume a small amount of phosphates during their reproduction and cell wall construction. It's a balancing act between too much phosphates (hello algae) and being completely devoid of phosphates (nitrifying bacteria dies off). You won't be at the completely devoid of phosphates end of that scale. No phosphate remover pad/ gfo etc is that good.
