Read that last post that Syd gave you,,, read it over and over.
If your truly doing the correct regimes your saying, then the problem your saying you have just doesn't exist,,, I don't see any problem.
I've had many people seek advice from me, and just about every time that someone has tested their nitrates to be high, I've tested their water at half the nitrate readings,,,,, this is because of people's perception of color shades, crappy kits and a very common mistake by most is leaving the vial with water and indicator to sit to long which increases the final readings.
If your fish are showing no signs of stress, stop worrying.
Besides, you've got tank full of super hardy fish.
As Syd mentioned, harder water will reduce your limitations,,, get your KH and GH around 8 minimum.
If your not over feeding, not over stocked, no waiste build up in substrate, keep filter maintenance on time and water change weekly then every thing should remain in reasonable check.
Get a brand new api liquid test kit and test your water again and after you've added indicator wait for exactly one minute then read the color,,,,, and that's your true reading as best your going to get from a fresh test kit.
Wait a few more minutes and your readings will show your nitrates much higher which will not be accurate as it's the mistake your probably making right now.
I do use a good api test kit. And the fact that aquotixs test is coming up the same 80ppm means that I'm not reading colours wrong. And aquotixs have told me to wait 5 minutes after the test to get a true reading.
