hi there. im new to this forum but not new to the fish keeping hobby. ive had tropical fish for the past 3 years. first i had a small 28 litre tank then upgraded to a 60 litre. i now have a 140 litre. ive had the tank set up or about 6 months. it has been hell so far. i can never get my water clean or stop it fromturning yellow. i have a fluval 405 filter with amonia remover, phosphate remover, as well as polishing pads to go with the normal sponge filter. i dont feed the fish an exessive amount or i dont have the tank overstocked. i have a couple of neon tetras, serpae tetras, columbian tetras, a bushy nose plec, and a chocolate zebra pleco (loved how hard these fish were to get and their looks so i decided to splash out on ebay ) ive even reduced my light times in th night even though i dont think the water conditions are alge related. i dont think it could be the filter either. i have a terrapin in a 200 litre tank with a fluval 205 and the water is always crystal clear. products you buy dont help either. i was thinking about going for an undergravel filter with a power head. do you think it would help?? cant go to my lfs because i know more about the fish there than they do. please help guys thanks