Thx for the reply, the reason for asking coincides with my other thread "Lighting issues". To add to both threads, the HC i added 2 weeks ago looks dormont, has gone dark green and looks poor, is wasn't until i reduced the depth of water on Saturday that it started to pearl, additional HC (New) added on Sunday tea time - still in their pots and they started pearling within 1 hour - difference in overall height of 1.5" approx.
Tank Dims: 39x18x15
Qty of water: 217ltr
GB gallons: 48.22
US gallons: 57.10
Current lighting 85 watts
WPG = 1.48.
E.I dosing as per article apart from an incease the powder in the trace mix details in other thread.
If I use:-
2 x 39 = 78 watts which would give me 1.36 wpg "WORSE THAN I HAVE NOW"
3 x 39 = 117 watts which would give me 2.04 wpg "BETTER THAN I HAVE NOW" increase of 0.52 wpg.
4 x 39 = 256 watts which would give me 2.73 wgp "OVERKILL"
with that luminaire it has two switch's,one each for two tube's.so you can only have 2x39 or 4x39.also i thought wpg was origanally worked out before t5's came on the scene(feel free to correct me if i'm wrong),and even though 2x39w is less than you have now t5's give out more light(again feel free to correct me)