No, that seems to be enough.
In my tank sponges only grow on shaded areas. When I put them into the light they melt away.
I still don't think they are responsible for the zoa decline. Zoanthids can be very finicky and aren't exactly beginner friendly. They also need at least a certain amount of nitrate and phosphate as other members have mentioned already. Weak zoas will get overgrown. If not by sponges then diatoms or something else.
You're throwing the towel hela fast.
Aquariums need a bit pacience. All of them.