Return pump question on gph

tankgirl2 · 05-04-2005, 04:42 PM

I'm setting up a 120G tank (4x2x2 ft) with built-in (gravity-fed) overflows and have a sump that measures 30x14x16 inches. The sump is rated for up to a 250G display tank (it says) but no info on water turnover - how much it'll handle.

Can anyone tell me whether that sump size would be a problem if I go with a Mag 7.5 or 9.0 return pump?

I'm assuming that the overflows will dump as much to the sump as the return pump sends up there (within reason), right? I'll use 3/4" return lines and 1.5" pvc for dual drain lines to the sump and will have Tunze Streams to hike up the display tank water movement, but I'd still like to have at least 10x tank volume/hour turnover from the return pump alone.

The only thing I can think of that might limit the return pump size is the sump size - is this right?

Tim224DT · 05-04-2005, 04:58 PM

Well i dont know if this will help you any with the sump GPH rating, My sump says its rated for a 75gallon or 300GPH. My little giant pump is pumping around 460GPH, Im not sure where they come up with these ratings.

Tim

motorslave · 05-04-2005, 05:21 PM

Well I would check the volume capacity of your over flows and then decide on a pump. Leave a little room for error ( dont put a 900 gph pump on an overflow rated at 900gph) so if something gets clogged you wont have an instand flood. How far apart the baffles are can create high velocity if they are too close. For my 150 I spaced the baffles 3 in apart and have an external pump rated at 850 gph. My overflow is rated at about 1500 gph. the volume through the sump is less than what the skimmer pump runs so all the water returning to the tank will be well skimmed.
The sump is 32x18x14, on my 55s sump the baffles are 2 in apart and the pump is 635 gph. The velocity is fine. If the velocity throught the sump is too much then there is better chance of bubbles making it to the tank. Do you have duel overflows? Somewhere there is a calculator to figure out how much your overflows can handle. HTH

Robert

autochek · 05-04-2005, 06:24 PM

On my 125 with duals I have them plummed with 1 inch to the sump. My sump has the same dimensions as yours and I'm using a mag 12 with 3/4 flex t'd to the returns. This is working great then I added a mag 12 on a SCWD for the closed loop.
The sump is also a refugium and the water isn't moving that fast thru it.
Tom

wharyat · 05-04-2005, 06:38 PM

If it is just going to be a sump, no refuge, you can put as much flow as you want through it, those 1 1/2" will handle close to 1200 GPH each.

craigGP · 05-04-2005, 11:27 PM

yeah, its usually the overflows that are the limiting factor, not the sump itself. you can always put a ball valve on the return line so you can slow it down a little if the sump isn't keeping up with the pump.

tankgirl2 · 05-05-2005, 11:37 AM

Really Great Info!!! Tim, Robert, Tom, Vince & Craig - you guys are the best!!!

How can I tell what the overflow is rated for? Is there a calculator somewhere?

It's not dual overflows, but a center overflow - polygonal, 13" wide at the back, 9" wide at the front, 7" deep, about 9 slots every 7" (slots are about 1.5" deep).

Yikes! My first big tank emergency (in 8 years) - woke up this morning and the pvc bulkhead fitting going to the return pump had broken (on my 260G). Sump drained all over the floor. Dead still water in the tank. Everything sliming. No salt water made.

I yelled for my husband, and then ran for some powerheads and an extension cord. Turned off the MHs. Got the powerheads going in the display tank. Then, ran for towels, and started disconnecting stuff under the tank. Meanwhile my hubbie had started bring in equipment - 32G trashcan on wheels that I make up salt water in. Wet/dry Vac, etc.

I had about 17G of RO/DI water for water topoff, and my husband has another RO/DI unit for his greenhouse with a 20G storage tank full. Also, my RO/DI unit makes about 6G/hr - started that right up. Enough water to start mixing salt water. We used the microwave to heat up glass bowls full of salt water - because the heater would have taken too long. While that's going on we're vacuuming up the water. My hubbie is one of those guys who has everything - including a spare pvc threaded fitting that would fit my tank (astounding because the tank is my hobby) - so he could fix the leak.

Within an hour we had the sump filled to it's normal level (it wasn't completely empty because the bulkheads are a bit above the bottom of the sump, plus there's a baffle that the water has to go over the top of before reaching the bulkhead fittings).

Astoundingly, the only thing I lost was a Tunze Stream because the controller for it got waterlogged. The two Mag18 return pumps, which had been running dry for who knows how long, were fine. Ballasts were fine.

I'm just amazed at how well we dealt with it, and how lucky we were that nothing shorted out.

tankgirl2 · 05-05-2005, 11:59 AM

Here's the fitting that broke.

The tank (I just quickly ran another stream across the top - will tidy up the cord later) then two of the sump - amazingly enough the ballasts are sitting on some loose tiles under the tank and I guess they kept the ballasts just high enough to prevent a short. You can see how close the electric plugs are to the bottom of the stand. I'm gonna change some stuff - finally mount those plugs on the walls of the stand.