What type of sump is recommended for a 210 gallon tank?

[John Hartford]

I want to keep the sump inside my stand which is 72" long by 24" wide and about 30" tall.

Is there a rule about sump size compared to the size of the tank or not really?

 

[Scuba_Dave]

Not really,
I've heard of a 600g sump on a 200g show tank
Many people run sumpless

So it depends upon what you want, what you can fit

 

[ddevlin]

I run a ETSS UHF 72 on my 200.

 

[sjm817]

A 75G tank would work well. Just add some baffles.

 

[kakan]

I agree a 75 of even a 55G would be a good choice for your tank it will also leave you with some extra space in your stand for other equipment.

HTH
Kakan.