After having trouble keeping the ammonia levels low in my QT a few weeks ago I discovered that the problem was the source water. The water coming out of RO unit gives ammonia readings of 0.25-0.50 ppm. Since I hadn't changed the RO membrane or the carbon filters in a long time I went ahead and replaced those. Readings are still the same. If I test my faucet water I get similar readings. I have been buying water from LFS which tests fine, but I'd like to fix the situation. Is ammonia something that an RO unit should remove? I was thinking of buying an RO/DI unit for the tank later on but I don't know if that will solve my ammonia problem. Anyone else ever have this problem?

The ammonia probably comes from your utility using chloramine, a combination of chlorine and ammonia to disinfect your drinking water. Ammonia pases readily through an RO membrane but the DI removes it. Here is an article Reverse Osmosis/Deionization Systems to Purify Tap Water for Reef Aquaria by Randy Holmes-Farley - Reefkeeping.com (http://reefkeeping.com/issues/2005-05/rhf/index.php#6) that you might like to read.

thanks carmie, ill read the article as soon as i get to my pc, im on the mobile now