My 90g has been running for 2 years and has a pretty large bio-load. I have never had noticeable PO4 or NO3 readings on either Salifert or Elos kits. SPS grows quite well in this tank and very seldom do I have issue with algae growth.
In the 225g tank however, SPS doesn't do crap. A few pieces do ok and others not so good. I am always having algae issues as well. P04 readings in this tank are undetectable and N03 are about 10 to 15.
Both tanks get 10% water changes bi-weekly, both have refugiums with DSB and large amounts of macro-algae. I have tried Tailored Aquatics Nitrate and Phosphate Destroyer; vodka dosing; and larger water changes on the 225g: with no positive results. SPS continue to struggle and algae growth has not been reduced.
The only difference I can see between the 2 tanks is the rock I used when setting up. The 90g was all live rock, while in the 225g I used a lot of BRS Eco-Rock. Perhaps there is a lot of phosphates bound up in this rock and continues to leach out.
