Advise Needed
 

Do you guys think a Dart is overkill for a 60 Cube? It will be for a close loop to a OM Squirt. This will be mostly a SPS tank.

I personally thing that would be good. Without head loss it would be 60x turnover. I have 75x on mine.

Closed loop pumps should be pressure rated. Dart's are flow pumps, not pressure rated...........

Why does a close loop pump needs to be pressure rated? What is the difference between pressure and non rated pumps?

You do not need a pressure pump for a closed loop unless you are planning on using educators which require pressure. Pressure pumps are designed for situations where you need to pump water up in height and have head pressure. Flow pumps are for creating flow and will not pump up very high. The dart will pump up to 12 feet, but the flow at 12 feet will be just about zero. At zero feet of head pressure it will flow almost 3600 GPH. A closed loop should have zero head pressure as you are not pumping water up above the water level in the tank. You will have some static pressure due to resistance to flow in the tubing your using and any elbows and fittings. If designed properly this will be minimal. In other words use 1.5" or 2 " tubing and keep elbows and fittings to a minimum.

Most closed loop systems run on Darts or other sequence pumps. I ran a CL on my 400 gallon for a while but got rid of it...now I have a bunch of nasty holes in my tank.

Gotcha.....................learn something new every day. I was always led to believe that you needed a pressure rated pump to run a closed loop, but alas, I was wrong..................