If the fixture comes apart I'd remove the top cover drill a few speed holes and throw on a pc fan.
I have this particular fixture on a heavily planted 20H with excellent results:I'm curious how these work out for you.
I am looking at replacing an older T-8 fixture for a 20 that I am getting set up for breeding M.Ramirezi or possibly M. altispinosa.
I could retro fit a t-5 in but LED would be cheaper in the long run