nitrates are driving me up the wall

[mike31154]

Yow, 25-30% water change per week, that's heavy duty. I do the same percentage but only about every 16 to 21 days. Why not start monitoring nitrate levels closely at the time you would ordinarily do a water change and extend a few days to see what happens? Take it one day at a time after that and if it gets out of hand, then do the water change.

Are you running the system with a sump? You mention bottled water, is the source reliable? Might want to do a quick TDS check on your source water, although you say there is no algae in your tank.... maybe that's the problem, algae takes up nitrates quite efficiently, but of course the wrong kind is a pain.l

[68shelby]

Yes I have a 45 gallon sump that will have a refugium in it as soon as I can get a light wired in. Right now the sump is basically 5-10lbs live rock rubble (inlet) under and over to the skimmer chamber then over to the refugium bed (currently about 4-5" of sand/gravel and then over into the return pump chamber.
And yes I have virtually 0 algae in the tank. even the back wall that I would leave for the tangs is bare other than pink and purple coraline. I wish I had some algae for the tangs.
Water flow is 2000 gph by the main pump,(probably somewhat reduced by the fact its in the basement) and I have 2 power heads one on each side of aquarium. 100g corner round.
Water I buy at sobeys. I have tested it prior to water changes and it tested fine. I am starting to think it is the mysis shrimp I have regularly fed.

[i have crabs]

how much rock in the tank its self?, i would invest in a ro/di unit so you can control your own water i woulnd trust buying water, not to mension the cost.
growing alge in a fuge will probably be enough to get the nitrates down from even the 20ppm mark but sound to me like there isnt enough filtering going on now