Question on return pump size

[KAS]

I have a 75 gal tank
About 4 feet of head (maybe a little less)
3/4" return line, flexible with 2 90 degree elbows

Right now I am using a Mag 7 and I am getting very little flow out of the return line (after adding in the head). Do these degrade over time? I cleaned it and tested it in the sink and got plenty of flow but who knows if I am getting the spec'd flow.

Should I replace it with another Mag 7 or should I go to a Mag 9? Last time I researched this and talked to Matt at Inland reef, we concluded a Mag 9 would be too strong, but now I wonder.

Space is really tight in my sump so I can't really change the footprint of the pump much.

Opinions?

ETA: The Mag 7 I am using has been running about 2 years now.

 

[RichConley]

according to reef centrals headloss calculator:

Total losses are 5.17 feet of head pressure, or 2.24 PSI. with a flow rate of 418 GPH.
It is acually probably less. Are you using flexible tubing, or spaflex pvc? If its tubing, you're getting restriction at the hose barbs.

You gain another 50 gph if you go to 1".

If you went to a quietone 3000 you'd have less energy usage, and go up to about 550gph.


Mag pumps in general are flow pumps. They DO NOT like head pressure, and perform quite poorly under it.

 

[astro1962]

Hi, I have a blue line 40 I had on my 75 that I bought at Johnnys in Providence about 3 mths ago. Im there every week so he can verify. I am looking to sell it along with other items if your interested, best reasonable offer. Contact me at russellinda@hotmail.com. Thanks Russ

 

[Scuba_Dave]

3/4" bulkhead too?
I went way over what I needed - dual 1.5" drains

It also depends upon how far "down" the drains are (depth of drain/overflow area), as water pressure will play a part in "forcing" water thru

I know algae & coralline have built up on mine, which would slow the volume down, except either return can handle 95% of the water draining volume

 

[johnbarr]

Is there a link to reef central calculator?

 

[smcnally]

Here you go:
http://www.reefcentral.com/calc/hlc2.php