I wouldn't veg with an HPS go get some 6500k cfls from walmart to at least supplement it with some blue light before using an HPS to veg. Also I am wondering which tetra you got? I also use tetra pumps and tried their smaller one on a single plant. As soon as I upgraded to at least a 50 for one plant I saw dramatic growth. The more aerated the water is the better the roots will grow. You can grow with four 25 watt cfl's from walmart per plant easily. I am investing in an 8 lamp t-5 4ft Tek Light, a hydroponics shop near me has them on sale for $409 which is a steal. 432 watts for 40,000 lumens and I can place the light about 4-5 inches from my plants b/c the ballast emits NO heat or noise and are located on the outsides of the fixture.