I've been running a Octo 5000 cone for about 2 yrs now on a 315 filled with large fish. I've been trying to get to a sps tank but PO4 levels will not stay down. No nitrate to speak of, but pO4 always goes back up to .1 ish. I am thinking of going to an ETSS skimmer hoping to break down more PO4. Any suggestions on the size? Anyone with similar issues?
I ran two 600 gallon systems that had worse PO4 issues - one hung around .12, the other aroun .22. Also no nitrate to speak of. One had an ETSS 1400 with Iwaki 100 pump, the other a monster MRC MR-4R recirculator.
I would not look to a skimmer for your solution unless there's something wrong with yours. FWIW, the cone shape is ripping you off of some significant capacity vs a
traditional cylinder shaped body. Cones and bubble plates are sales gimmicks that add little to nothing to performance. Not sure I'd necessarily use that as a criteria for changing skimmers either since you already have it in place.
If you feel you must upgrade, i would go for a better needle-wheel like those linked above. The MRC and ETSS designs are a bit old fashioned at this point. Not that they do not work, just that they take up a lot of space vs the needle-wheels. That doesn't account for the increased time to maintain these designs - which is another minus.
If you aren't already maybe try wet-skimming for a few months and see if you make any headway. You will get more waste out that way. Likewise if you can commit to more frequent cleanings. A dirty skimmer is like a skimmer with one hand tied behind its back.
Also, if your sand bed is more than a few years old, i'd also consider looking there - possibly replacing it altogether. (Or eliminating it.) it's a likely place for excess nutrients to collect and it's very cheap to replace compared to most other possible solutions.
-Matt
