Water testing nitrate high

[alddb]

I have an established system of 3 years. No deaths in past 6-7 months (lost a snail then). lPS says leave numbers alone because fish are happy and no deaths. But it bugs me. I have always had high nitrates and phosphates. I have gfo reactor. I have a protein skimmer. I have a sump. I tried cheato twice and just melted. I have no algae.
Using Hannah I have
7.6 PH (I have been buffering to raise to 8.0)
.19 ammonia
.90 phosphate
75 nitrates
0 nitrites (api test)
.026 salt.
78 degrees

I have been using nopox to no change.

 

[I never finish anythi]

How big is tank ?
How much live stock ?
How often do you do water changes?
Where do you get the source water from ?
Sorry for the questions lol

 

[Timfish]

If this was my tank I would be doing larger water changes and fiddle a little bit with t he amount of food I was feeding daily to reduce the nitrates and phosphates. I'm not surprised you don't have much nuisance algae, I've rarely seen any correlation between nuisance algae and testable nutrient levels. I'd stop the nopox, it's just a labile DOC suppliment and there are risks involved in using it. You likely haven't seen any effect as your system likely has cryptic sponges that can remove labile DOC much, much faster than the bacerioplankton in your system. (I know this is heresy but I'd turn off your skimmer too.)

Be sure not to bottom out your nutrients, especially phosphate. Corals love urea and ammonia from fish but nitrates can interfere with their calcification. However, this paper (among other) shows low phosphate has severe impact on coral's photobiology. FWIW .03 mg/l is the minimum, .5 mg/l is acceptable and even .9mg/l might not be an issue.