Overkill for a 200L tank?

Is it this one: http://www.seapets.co.uk/products/a...a-200-aquarium-and-cabinet-oak-and-wenge.html If it is, a 2 bulb FishNeedIt or Coralife T5HO light would give you about 30 micromols of PAR, which is low light, so CO2 isn't essential. I'm not sure what light fixtures are available there, and I doubt that we have any PAR vs distance measurements on them anyway.

Its not a brand new tank its quite an old one; the dimensions of the tank are
120X36x45

and the site where the light was from
http://www.guppysaquariumproducts.c...-610-long-individual-reflectors/prod_633.html

The 45 cm high tank would increase the PAR with Coralife and FishNeedIt lights to about 40 micromols. That 6 bulb light doesn't look like it has good reflectors - the bulbs seem too close together for the reflectors to be very effective, and there isn't enough room between the bulbs for reflected light to get through. That makes me think it would be roughly equivalent to 3 side by side Coralife 2 bulb lights, so you might get 3 times the PAR with that 6 bulb light. That would be far more than you could hope to supply sufficient CO2 for the plants to use the light. But, with 3 power cords you could run just 2 bulbs, and probably be fine. You could run each pair of bulbs for 1/3 of the photoperiod, which would stop any tendency for the plants to all grow towards one set of bulbs.