Help, i cant get my nitrates down!

[Trucker84]

So i have this 100gal tank. It was the first tank i bought, it came with some fish, i got it off craigslist. Well for a long time i didn't understand the importance of regular water changes. The glass never got dirty, so i figured everything is ok.

So anyway, my nitrates are around 40ppm. I've been working for about 3 weeks now on it and haven't seen any change. I started off doing 25gal waterchanges every other day, and i added a nitrate remover filter media made by fluval to one of my filters. That didnt seem to change anything, so i've been uping the amount of water i change. I am now doing 40gal every 3 or 4 days and still seeing no change. I havent done more than 40gal cause thats how much water the res. for my RO holds. But i feel like i have heard that it's not good to change more than 50%?

Any and all advice is very much appreciated.

 

[toehead11183]

How many fish,
Fish sizes,
how often you feed,
Salt or Fresh?

 

[Trucker84]

11" Xingu I Pike, 8" Wolf fish, 12" pleco, 6" arowana, 5" S. Am. Bumblebee cat, 10" ornate bichir, 5" bumblebee cichlid

i feed mostly thawed shrimp or bait fish, some jumbo krill and pellets in AM and PM

 

[TwistedPenguin]

You don't mean that you're using straight RO water, do you? That's not a good idea just in case you are. Is there any reason you can't just use regular tap water? The fish you named would most likely deal just fine with your tap unless it's unhealthy for your consumption also.
Just to make sure-the paper test strips are worthless. The API Master Freshwater test kit is the best to use, it's a liquid test tube kit. Is that what you're using? If nitrates were 40 then a 50% water change should drop them to 20 ppm. That's a LOT of huge fish in just a 100 gal tank. I don't think there's any way you're going to be able to keep up with the nitrate creep on that tank with the tiny water changes you've been doing. I'm pretty sure that's why they're not going down. All that protein you feed won't help either.
My suggestion is to use your tap water with a declorinator (if you need it). Straight RO water is bad for fish.

 

[Mattyou]

When you do your water changes are you gravel vacuuming? When is the last time you gave your filters a GOOD cleaning? Got sponges or floss that is holding on to 3 month old crap? I think you may need to feed a quality pellet (your choice) and use all that krill / shrimp / bait fish 2-3 times a week as treats. Also, reduce feeding to 1 time a day. If that does not help, move a couple of fish.