water drywall cloudy

I've got a problem, hopefully someone can help. Specs first: 10 Gal with full hood / light Aquaclear HOB filter DIY C02 EI Dosing ( less than recommended ) Tank has been set up since Dec 2009 Water ( API Liquid Test ) Ammonia 0.25 or less Nitrite 0 Nitrate 20 Ph 7.6 ( until recently, 6.8 )...