Originally Posted by migdem
oh sorry about that. I have 4 tubes in total of 54 W each that means 1.8W/gallon. They changed the model and I got the new one with 4 tubes. The problem is that if I cut by half the light in the aquarium is not so nice because it becomes dull because on the back there will be light but on front nothing and same if they are reversed.
OK, I just did a calculation, your 450 litre 5-foot tank is about equal to my 115g 5-foot tank.
This is difficult for me to advise, as I have never bothered with CO2. And, the watts per gallon is somewhat useless, esp with T5 HO light.
I have experimented with T5 HO lighting, two 48-inch tubes (54w each) over my 115g. For my purposes, it was way too much light. I went back (after a week's test) to 2 48-inch T8 tubes, 40w each. Though again the watts is rather meaningless. The intensity is more important, and one T5 HO tube is approximately equivalent to 1.5 T8 tubes of the same type [e.g., Life-Glo 2]. So two 48-inch T5 tubes give the same light intensity as 3 T8 tubes. I only have two T8 tubes and it is adequate for my plants, and without additional CO2.
From this, I would assume that with CO2 and increasing fertilization to balance, you would need 2 to 3 48-inch T5 HO tubes. I assume youhave 4 now, and you had a real algae problem. That suggests there is too much light intensity to balance the nutrients.