Size of sump for 90 G ?

[Aquattro]

Ideally you want something bigger than 29g for a sump. Power outages may very well over flow the sump, depending on your drain config and sump water level. And 2600 GPH thru a 29 might be a bit much.
For my 90, my sump is 110g, but you could probably get away using a 40g.