High nitrates will not go gown

[Reefer1485]

So for some reason my nitrates will not budge from 20ppm. I have done large water changes feed LRS reef frenzy nano once daily, running protein skimmer, filter sock on one side, caddy on the other with nitrate filter with filter floss and chem pure blue. My phos are steady at .04 but just can’t get my nitrates down. Here is what I have in it:

20 gal IM AIO
Two clowns
One bi color blenny
Two peppermint shrimp
One cleaner shrimp
Turbo snail
Another snail can’t remember the name of it
7 herms
One pistol
15 pieces of coral

just did a 4 gallon water change and I change out the filter socks every few days. The corals look good but just can’t beat this brown algae and I think it’s due to my high nitrates

what are your thoughts?

 

[Reefer1485]

Total water I have in it is about 12 gals. Live sand, two big pieces of live rock with my other rock. Tank has been running since beginning of September last year

 

[fishhead1973]

Kind of over stocked you may be able to overcome this. A good skimmer and some carbon dosing. Only use half of the recommended dose for a while. And you should see results in a week or two.