I think it would be fine, the ponies like to be able to get higher from my experience but its not a necessity in some species. Tak raised as you know is the only way to go and tank size would be fine. Be ready to do alot of feedings. If I did a seahorse tank over again I would go bare bottom , if its gonna be a dedicated zoa, pony tank just make sure they have some sort of plant rather it be real or fake to hitch to. Sounds like a cool idea and I look forward to you coming this way to grab your ponies....hint hint