750XXL Drain Line Plumbing

Uglyknob · Dec 22, 2019

Hello, everybody.

I have a 750XXL that I've modified the return plumbing on. It is 1" SCH40 with 2 X 45° elbows. The output nozzle is a VFG with the VFG part removed because of their restriction.
I am using a Varios 8 pump.

My problem is that I've overwhelmed my drain line. I have the stock RSR drain valve on there cause I never had a problem with it and now it is wide open.

Of course, I've turned the pump down to where the valve is wide open and I'm maintaining quiet. However, I'd like to be able to turn it back up.

Is the RSR drain valve restrictive? Meaning, I know a lot of folks have switched to the gate valves, but I don't want to bother with that unless it will increase my drain line capacity.

I am only at level 3 on the Varios 8 and already overwhelming the drain, so a little disappointed in that.

Thanks for any and all help.

Ron Reefman · Dec 23, 2019

A wide open 1" drain that is gravity fed with no elbows will only flow a little more than 960gph. How much is your Various 8 pumping at level 3?

			Assume Gravity to Low Pressure. About 6f/s flow velocity, also suction side of pump	Assume Average Pressure. (20-100PSI) About 12f/s flow velocity	Assume "High Pressure" PEAK flow. About 18f/s flow velocity*
Sch 40 Pipe Size	ID (range)	OD	GPM (with minimal pressure loss & noise)	GPH (with minimal pressure loss & noise)	GPM (with minimal pressure loss & noise)	GPH (with minimal pressure loss & noise)	GPM (with significant pressure loss & noise)	GPH (with significant pressure loss & noise)
1/2"	.50-.60"	.85"	7 gpm	420 gph	14 gpm	840 gph	21 gpm	1,260 gph
3/4"	.75-.85"	1.06"	11 gpm	660 gph	23 gpm	1,410 gph	36 gpm	2,160 gph
1"	1.00-1.03"	1.33"	16 gpm	960 gph	37 gpm	2,220 gph	58 gpm	3,510 gph
1.25"	1.25-1.36"	1.67"	25 gpm	1,500 gph	62 gpm	3,750 gph	100 gpm	5,940 gph
1.5"	1.50-1.60"	1.90"	35 gpm	2100 gph	81 gpm	4,830 gph	126 gpm	7,560 gph
2"	1.95-2.05"	2.38"	55 gpm	3300 gph	127 gpm	7,650 gph	200 gpm	12,000 gph
2.5"	2.35-2.45"	2.89"	80 gpm	4800 gph	190 gpm	11,400 gph	300 gpm	17,550 gph
3"	2.90-3.05"	3.50"	140 gpm	8400 gph	273 gpm	16,350 gph	425 gpm	25,650 gph
4"	3.85-3.95"	4.50"	240 gpm	14,400 gph	480 gpm	28,800 gph	700 gpm	42,000 gph
5"	4.95-5.05"	5.563"	380 gpm	22,800 gph	750 gpm	45,000 gph	1100 gpm	66,000 gph
6"	5.85-5.95"	6.61"	550 gpm	33,000 gph	1100 gpm	66,000 gph	1700 gpm	102,000 gph
8"	7.96"	8.625"	950 gpm	57,000 gph	1900 gpm	114,000 gph	2800 gpm	168,000 gph

AZMSGT · Dec 23, 2019

The part that connects to the drain pipe bulkhead is the main point of restriction most likely In your system. That Red Sea part narrows to 25mm-3/4”.

FWIW, allot of people that own the 750 & 625 (same plumbing) have very successful tanks with stock flow. My point is don’t worry about it to much.

Uglyknob · Dec 24, 2019

I am after more filtration as I have some dirty fish. I keep freshwater in the 750. It is not a marine tank. I came here because there aren't many folks that have used the 750 for that on other forums and there is a plethora of info for it here. That is how I found ways to redo some of the plumbing, get the VFG, etc.

I don't think I am getting anywhere near 960GPH, and I haven't seen a flow chart for the Varios 8 that shows flow for each setting, only the max. I'd be shocked if anyone was actually getting 960 out of a 750XXL though.

Most of it is sawdust from my pleco though. It is only a bristlenose, but he is turning my driftwood into waste at an alarming rate. I may have to rehome him. There are 2 3.5' long by 1' high logs of driftwood in there.

I may just add an FX6, as I have a spare in the garage not doing anything, but I really didn't want the hoses in the tank.

I've got a swirl going on both ends of the tank that leaves some debris right in the middle of the tank at the front. I feel like, if I could get just a bit more flow, it would carry it around and eliminate that deadspot.

As far as the sump and flow goes, I don't need any more for chemical filtration. The levels that concern me are nil. No ammonia or nitrites and my nitrates stay almost nil because of the plants. I have filter cups in there, all filled with poly.

Thanks for reading and helping! Oh and Merry Christmas Eve!