[tjcharnley]

So I have a 75g Oscar/JD tank. One of each pretty medium sized nothing crazy.
Just been tinkering with getting my filter setup right.

Water comes in and goes immediately into the biomax around the outside ring of the bottom of the filter, comes up through the coarse mesh that comes with the filter, then down through the coarse round black, with the red basket removed and filled with matrix, then into the next basket flows through as follows; matrix, down to purigen, then the fine round black, and then back to the tank.

tank as always been crystal clear and all levels good except doesn't matter what amount of often I do a water change I can't get the nitrates to come down much below 20ppm.

did a lot of research and this is what I gathered with what I read.
Will this be a decent setup?

Amounts

stock amount of biomax
250ml ( 4 fine bags worth) of purigen
2l of matrix

how's that going to do ?

also again its a fx4 setup

 

[Auballagh]

Hmmmmm.....
I guess things continue with this setup?

https://www.cichlid-forum.com/phpBB/vie ... 3#p3142213

Okay then. As the ever redoubtable 'Oscar6' and I both recommended to you earlier in the SA section of the forum, your 75G sized tank is just too small in size to keep one Oscar in it long term. Let alone your JD and the Oscar. So, we'll just call this a 'grow out' tank for now, okay?
That said, I believe your FX4 canister filter is working beautifully. Nothing wrong there. And, though I'm not much of a fan of Seachem Purigen.... it DOES do a nice job of polishing your water clarity. IT DOES NOT do very much in removing Nitrates from your water.
And if indeed, your Oscar and the JD are just 'mid-sized'. Then they are still young fish, and have a bit of growing to do. And as young creatures tend to be - they're hungry most of the time. And well, they eat a lot.
And, you wind up with a lot of organic compounds in your water. That is.....
Nitrates.
And, it seems your growing New World Cichlids, are outgrowing their 'grow out' tank. You don't actually disclose how much of a percentage of water you're pushing, or the actual frequency of water changes you are doing for this tank. But, I suspect it is something less than 85 to 90 percent, at a rate of twice per week that you will probably need to perform, to keep this small tank under 20 PPM in measured Nitrates.
Yep.
And that's just one, basic reason that much larger tanks are recommended for keeping these large, New World Cichlids.
But well, there are some things you can try to slow down, or at least limit the buildup of Nitrates in your water.
- Bigger aquarium.
- Less Food. (with young, New World Cichlids though... that might be a bad idea).
- Install foam pre-filters on all filter intakes. Clean all pre-filters 3 times per week to remove uneaten food and fish waste products before that stuff breaks down into toxic organic compounds.
- Use plants in a modified, in-tank refugium set up, as shown here:

https://www.cichlid-forum.com/phpbb/vie ... 0&t=379578

- Install a full-up/heavily planted, above-tank plant refugium.
-
Otherwise, you are now facing the reality of what owning large-sized fish in an aquarium means. And yes, those fish of yours are living in their own toilet. And like almost all of us have, your aquarium is also a closed loop system without the benefit of an unlimited supply of non-chorinated water to push into and over-flow/drain out of the tank (well water - 100% plus water changes, daily!).
Or, as I've said before.....

THE SOLUTION TO AQUARIUM POLLUTION - IS WATER DILUTION.