Nitrates spiked in two tanks

[dlsrks]

I have two saltwater tanks, one 75 gallon which is 3 years old, and a 29 gallon which is 3 months old. The nitrates have spiked in both tanks. In each tank, I have done two water changes. when that didnt work, i cleaned the filter/sump. When that didnt work, I used water conditioner to lower the nitrates but the nitrates are still around 40 ppm. In the past, they have always been 0 ppm. I have my own RO/DI system. I have tested the RO/DI water and the Instant Ocean Salt Mix. Both are at 0 ppm. Cant think of anything different I am doing beside my recent purchase of Marine Snow. Is it possible that it has any nitrates? Or would a better grade of carbon help? Any comments would be appreciated. Thanks.

 

[bavass]

can you tell us more? what filter system you running? how often are you changing water? how much are you feed? etc... powerheads....

 

[dlsrks]

In my 29 gallon, I have a fluval 305 filter and two small powerheads. I feed them some flake food daily and 3/4 of a cube of brine shrimp about every two or three days. Only have a couple of corals in there so I don't add much coral food if any.
For my 75 gallon tank, I have a 75 gallon sump with a coralife super skimmer. I feed them the same way but they get 2 cubes of brine shrimp seaweed daily for the tang and angelfish. There are quite of few corals in there so I add coral food about every three days.
I haven't changed how I have fed them in the last year but don't understand why the nitrates have stayed high after all the water changes. I change out about 12 gallons a week on the 75 gallon and 6 gallons a week on the 29 gallon. What do you think?

 

[bavass]

I stopped using canister filter because if you don't clean them every week they become nitrate factories, i also feed a 55g 1 cube every other day that has been rinsed to remove nutrients. The nitrates and or phosphates have built up over time. When mine were high and i am talking 160+ ppm. I did 50% water changes till i got to 20 then started doing 15g a week water changes now i am down to 7g a week

 

[dlsrks]

The big tank that has a sump seems to be doing better. I will keep that in mind about the canister filters. Thanks.