Also, how old are your test kits. I noticed the same issue with both of my tanks. The test kits were saying that my nitrates were 20-40ppm, even after 20-50% water changes. I figured out that the two test kits I had were old and my nitrates are around 5ppm or less.

I agree with the other guys on using better salt. I currenty use Reef Crystals, which seems decent. However, I'll probably switch back to Red Sea Coral Pro. I just like the salt better for some reason.

I have about 35-40lbs of LR in my 24 gallon Aquapod and 20lbs of LS. This also helps with my filtration. I'm not running a skimmer. Anyways, good luck and hopefully you could figure out how to drop your nitrates.