Par 38 options

A Par38 is generally good for a square foot area so you are going to need a lot more than that. You are probably better off doing a DIY LED canopy with Cree XM-L or Cree XT-E.

See my Par38LED Tracklight link in my sig line.

If I was going to do a tank the size of yours I'd agree with 5. I'd stagger them 3 in a back row 2 in front between the back 3.

You'll want bulbs that re dimmable and you'll ned a way to adjust height. I'd suggest Cree LEDs.

I also suggest 60 degree lens as a min. If I ever redo mine I'd go wider lens that I bought. But a year ago you could not find a Par38LED that was dimmable.

The nice thing about the track light vs.a ceil outlet or can fixture is I have options to move left to right. It takes a bit more creativity to aquascape but I think it's worth the effort.