You'll need 2. And I highly suggest the wide angle lenses to avoid the hotspot you get with a 90. (not sure why they don't include the wide's in it, probably to get ya to spend more money )
A Radion xr30w Gen 3 Pro at 11" above tank gives you a 30"x30" spread so you'd need two. The xr15w is your best bet for perfect coverage but if the budget allows I'd go for two xr30's because later if you upgrade (as everyone does [emoji6]) the xr30's will give you the extra coverage you need on a bigger tank dim
Curios if all of you are happy with your XR30 Gen2s? I can't say that I am with respect to SPS. Grows the basics birdsnest, stylo like crazy, but have trouble with nicer ones.