imo its not a matter of what brand, like you dont NEED ati by any means, but they are certainly one of the best, if not thee best... the tek lights are great and EVERYONE (well basically) seems to have good results with them... at 20" your tank isnt a 90, i think a 75 like mine... my self you could say i have too much light, or at least more than is needed... i have a tek light, the 8 bulb 48" fixture... i think you would be fine with a 6 bulb, and i would get that over the 4 bulb... i got my 2nd teklight, the one i am speaking of when i upgraded in january... personally, i am very happy with this sunlight supply company, the maker of tek lights, and plan on purchasing my retros from them when i upgrade to my next lighting setup, which will also be t5... the price is great too as i get mine from BRS, which is actually cheaper than buying them direct... for my 8 bulb fixture and all new bulbs, with a 25% off the bulbs when you buy a fixture special BRS has at this time, it cost me about $502 shipped... and i am very pleased with every thing about it... my spread and coverage, ability to setup the bulbs and spectrum at will, and its penetration (as i have had sps which where not new to my system, 2" from the bottom, amd bleach when i change even a few bulbs in the bulb configuration)... again, the 8 bulb is overkill, but i would get the 6 bulb if i were you, or at least i recommend them greatly... GL