Originally Posted by humblepie
Not really. Those flow numbers listed are always the theoretical max output of the pump pushing water by itself. If there is any restrictions, such as media in the way, then the pump is going to go slower, thus less flow. Usually, the true flow rate on a filter is usually half or less of the stated flow rate. Rule of thumb I was told and use is to take whatever flow rate is listed and use 40%-50% of that number. So a canister filter with a 370gph flow rate is going to have an actual flow rate of 148-185 gph usually when filled with media. (more restrictive media will have less flow)
Typically, you want to turn your tank at a minimum of 3 times per hour. So you take 180 gallon tank and you'll want to be moving 540 gallons per hour at a minimum. Some advocate more. I have a friend who swears by 10 times the turn rate. You really don't need THAT much flow in my opinion.
So if you are using the 303/403/CF-400 models of the sunsun/aquatop filters then you are going to need 3 of them. If you are using the 304/404/CF-500 models then you are going to need 2 of them for a tank that size.
I have the Aquatop 500 model (rated 525 g/p/h) on my 90, and it works very well. That said, my setup is probably about the limit. Any larger tank I would have to recommend more filtration. I would go for two of the 500 models in your case.