Wet/dry filters don't remove nitrates. It only converts ammonia to nitrite, and nitrate to nitrates. Take a water sample of both your tank and tap to your LFS just to confirm your measurements. If it's truly 80ppm, I suggest getting a DI/RO filter and using a lot of plants on your tank. However, you would need stronger lighting (regular fluorescent will result all your plants turning yellow/brown and dying over a couple of week) and CO2 injection.