nnitrates too high

[Galvan]

I have a 75 gallon tank with 80lbs LR and about a 3 inch bed of sand. have the sump along with the protein skimmer. Three 900 maxi jet and 1 rio 3100 return pump. Tank is 1.5 years old. Tank contains:
1 green mandarin
1 blue hippo
1 yellow tang
1 damsel
1 coral beauty
1 royal gramma
1 maroon clown

1 poly
1 mushroom

Problem has always been that my nitrates are reading from 80-160. With a water change can get to about 40+ but then they start to climb. Do water changes 20 gallons every month tank is always clean. not sure what to do any more. attaching some pics

 

[WRASSER]

What tends to happen is the live rock absorbs the nitrates, so when you do a water change once a month the new water absorbs the nitraes from the rock and the fish and things put it back into the rock. IMO you should do a large water change, then a reg. change like once a week or til it comes down to were you want it.

 

[Galvan]

Is the amount of fish O.K. for my 75 gallon.

 

[WRASSER]

The Hippo is going to out grow the tank, with that said It is Ok for me. Some people will disagree. The two tangs and the clown are large fish and should be in bigger tank. The angle kinda makes it a little crowed too. You have open water fish in a small tank.
I also say enjoy it while you can and when the time comes to take out fish take them out :wink:

 

[waymack97]

tangs equal a lot of poop. may be you need just a little more live rock also. one and a half pounds per gallon is about right.
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[Anonymous]

My

...that large filter block in the sump and the live rock could also contribute to the nitrate problems as they are great detrious traps.