If your tank is only 20" long why are you using such long t5 bulbs? 56w bulbs are like 4 feet long. If the mh is 300w that will be plenty of light. But make sure you have it high enough over your tank. If its 150w i would def use a t5ho to supplement. Lunar lights dont matter as far as wattage goes... They are usually less than 1w anyway. Give us all the info about the lights and i can give you a better answer
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