If you're going to have 200g of stocked tank, the 9 is the smallest I'd go, and get a new sump if you have to. The recommended sizes for all of these are a sales pitch IMO.

Plus it's not much more money then the 7 and then you open yourself up to adding more volume if you ever need it like a frag tank or external Refuge etc.

Yupp if you're going stocked you need to double the rating with most skimmers available to the masses.

You are going with a 20g sump on a 175? You may want to rethink that unless space is an issue. make sure you have enough room for a power outrage, 20g is a tad small for a 175.

Have you calculated if your 20g can hold the back flow of water when the return pump shuts down? A larger sump is cheap insurance and won't limit your equipment choices. Will also give you room to upgrade down the road for adding reactors or other such things.

I busy eating and see Ray has the same concern!

Didn't have much choice for the sump-kinda came with the tank lol.

I haven't set anything up yet-still in the planning phase.

If you have room, I'd upgrade that a bit. Depending on your setup, a power outage could easily flood that sump.

I've been keeping my eyes open for a 40g/50g tank I can modify into a sump with fuge.

Anyone heard of the new Coralbox DC Curve Protein Skimmers?

Runs with controllable jebao pumps.