stanlalee
Active Member
your calculations are fine, its just the watts per gallon rule of thumb doesn't work. for example I have 10 watts per gallon and 300w of metal halide power. thats probably less intensity than a high end 39wx4 36" T5 fixture and equal to an average one which comes out to 5.2 watts per gallon. No amount of pc would equal the intensity of any of the above regardless of wattage. there isn't enough room over the tank to fit that many and they dont penetrate well. T5, VHO, PC, MH all have their own specific rules of thumb and thats before considering bulb and reflector effectiveness which can change everything. A 175w 13k AB has more PAR than a 250w XM 20k and a 250w XM 10k has more PAR than most 400w 20k bulbs. a lumenmax elite or lumenbright can tripple the output of a batwing reflector with no other changes. to sum it up the watts per gallon rules are useless to use universally and almost as useless when comparing apples to apples (halide to halide) once you factor in all the othe variables.
With T5 HO and decent reflectors 4 tubes the length of any tank 18" or less front to back (and depth of 24" or less) is sufficient to provide full coverage and enough intensity keep anything wether it be four 48" 54w tubes over a 48" 55g (or 75g), four 36" 39w tubes of a 36" 30g or four 24w T5 tubes over a 24" long tank. A tank wider than 18" front to back could use additional T5 for coverage.
Metal halides have their own general rule of thumb: one halide per 2'x2' area. wattage based on depth: 150w/175w up to 20", 250w up to 24+", 400w/1000w up to 30+"
PC yet their own, the most important dont expect stellar results with SPS or deep tanks. two bulbs across are usually sufficient for most LPS/softies.
VHO require four tubes to keep SPS and four tubes of VHO will have a high watts per gallon inherently (48" VHO bulb is 110w, twice that of a T5 HO). intensity is somewhere between T5 and pc.
With T5 HO and decent reflectors 4 tubes the length of any tank 18" or less front to back (and depth of 24" or less) is sufficient to provide full coverage and enough intensity keep anything wether it be four 48" 54w tubes over a 48" 55g (or 75g), four 36" 39w tubes of a 36" 30g or four 24w T5 tubes over a 24" long tank. A tank wider than 18" front to back could use additional T5 for coverage.
Metal halides have their own general rule of thumb: one halide per 2'x2' area. wattage based on depth: 150w/175w up to 20", 250w up to 24+", 400w/1000w up to 30+"
PC yet their own, the most important dont expect stellar results with SPS or deep tanks. two bulbs across are usually sufficient for most LPS/softies.
VHO require four tubes to keep SPS and four tubes of VHO will have a high watts per gallon inherently (48" VHO bulb is 110w, twice that of a T5 HO). intensity is somewhere between T5 and pc.
