Return Pump Lack of Flow

[Nick Rose]

I Use the Mag 9.5 for my return pumps. One on a 40 gallon and one on a 90 gallon. I have always noticed a lack of flow with the one on the 40 gallon. It hasn’t bothered me but today I decided to take a look. I took it out and took it a part to see if there is anything blocking the impeller and then I checked the pipes and all clear. Then I swapped this one with the one on the 90 gallon and still a lack of flow but on the 90 gallon it’s a strong flow. Any idea why the lack of flow?


This is the 90 gallon tank. The first vertical is 20” the horizontal is 12” and the last vertical going into the tank is 23”. There is 3 unions 3 90 degrees and a check valve.

This is the 40 gallon tank. The first vertical is 16” the horizontal is 13” and the last vertical is 22” and another horizontal of 6”. There is 2 unions and 3 90 degrees and 1 Ball valve.

 

[Billldg]

Have you checked the ball valve on the 40, maybe its partially closed, maybe a internal malfunction or debris. Plus it looks like the 40 has 3/4 pvc, what is on the 90, is it 3/4 flex also or 1 in.

 

[Nick Rose]

I checked the ball valve and its fully open and no debris. The 40 does have 3/4pvc and the 90 also has 3/4pvc, none is flex. What is odd is both basically have the same or close to same horizontal and vertical lengths. I did notice that there was a i guess a slime coating the inner walls of the pipe. But I doubt that would cause a dramatic loss of flow.

 

[Billldg]

The only logical thing I can say is that somewhere, somehow their is a restriction of some sort, same pump of both tanks with different results, odd to say the least. You ruled out the pump because you switched it, this is definitely a headache maker.

#reefsquad, any suggestions?

 

[Peace River]

If you think about the internal diameter of the pipe (not the external diameter), is it possible that there is a restriction at a joint?

 

[Nick Rose]

I checked the whole length of the pipes, checked the joints, the elbows and no restriction. I was thinking of getting some vinyl tubing and barbed fittings to see if one continuous tubing would do better.

 

[Mastiffsrule]

Evening

Sounds like you ruled out the pump itself, and the pipes are clear. The 90 bends should not make that big of a difference from tank to tank.

My thought would be a restriction at either the return nozzle or intake. Same return nozzle on both? In the sump of the 40 is there anything around the intake that may slow down flow, like a clogged sponge or thick Matt of cheato?

Last thought would be the drain side. The overflow boxes and the hoses flowing freely on that side?

 

[Nick Rose]

I just noticed that the loc line on the 90gal is 1/2” so it goes from 3/4” pvc to 1/2” and the one on the 40gal is 3/4” loc line. Would this make the difference. I have also attached a video of both returns. Also I wonder if I’m being too picky. If you look at the overflow on the 40gal it seems at a good level.

 

[Peace River]

Yes, that is the type of reduction that I mentioned previously. It may or may not solve the whole issue but it should definitely help!

 

[Nick Rose]

So I'll put on a 1/2" loc-line and see if that helps.

 

[Peace River]

So I'll put on a 1/2" loc-line and see if that helps.

Did you mean 3/4” loc-line on both? It would seem that you don’t want to reduce from 3/4” pvc to 1/2” loc-line. Did I miss something?

 

[Nick Rose]

The 90gal goes from 3/4" pvc to 1/2" loc-line which is the return in the beginning of the video. The 40gal is 3/4" all the way.

 

[Peace River]

it sounds like you have probably figured it out. If you think about taking a garden hose and stepping on it in the middle you will restrict the amount of water coming out the end. If you take the same hose and put your thumb over part of the end of the hose (without stepping on it) you will actually still be restricting the flow but will create a more powerful water jet that you can feel. I think this may be what is happening in your tank. Hope this helps.

 

[Nick Rose]

So now with that figured out is it better to have the more powerful water jet?

 

[Peace River]

So now with that figured out is it better to have the more powerful water jet?

Good question! Do you want more turn over of water or more water movement?

 

[Nick Rose]

I don't know. I believe I'm good on flow. I have a IceCap 1k Gyre that is running at 30% and it seems like there is good flow. The turn over seems good. If you look towards the end of the video you can see where the water line is with the overflow teeth. If I wanted more turnover I assume that means getting a more powerful pump.

 

[Peace River]

I don't know. I believe I'm good on flow. I have a IceCap 1k Gyre that is running at 30% and it seems like there is good flow. The turn over seems good. If you look towards the end of the video you can see where the water line is with the overflow teeth. If I wanted more turnover I assume that means getting a more powerful pump.

Not necessarily. If my understanding of your situation is correct then if you use a 3/4” loc-line then you will remove the restriction and have more water volume moving into the tank. If you use the 1/2” then you will restrict some of the water and the water that moves through the loc-line will go through with more pressure in a smaller area which feels like more flow and will create more water movement.

 

[ca1ore]

It’s flow versus velocity. Restricting the outlet will increase velocity but reduce overall flow. Depends on what you are trying to accomplish. If max turnover, then ditch the 1/2” lock line. If most surface agitation then keep it.

 

[Nick Rose]

The 1/2" is on the 90 gallon this was not the problem tank. The tank that was the main focus is the 40 gallon with the 3/4". I think I will just keep it as is.

 

[Peace River]

The 1/2" is on the 90 gallon this was not the problem tank. The tank that was the main focus is the 40 gallon with the 3/4". I think I will just keep it as is.

Sounds good! And now you know why there appears to be a difference in the flow rate!