Increased flow causing overflow issue

[fijiwigi]

I redid the plumbing for my return line from my sump into my tank. I had 1/2" hard PVC with elbows and a barbed end type flow director. I changed it to 3/4 vinyl tubing with Locline plumbing and 2 locline pipes with flow directors. This increased my flow rate which is great. I have a mag7 pump with head height of 4feet the vinyl tubing is about 5feet MagDrive Flow Chart Based on this calculator 4' is 480gph and 5' is 420gph

The problem I am experiencing is it seems as if my overflow can not keep up now. the tank level gradually rises to where I am concerned that the tank may overflow so I turn off my pump. This is my overflow New Acrylic Overflow Box and Skimmer Box for Saltwater Aquariums It is rated to handle 700 gph on a 75g tank with a mag7 and 500gph on a 55g tank with a mag5. I have a mag7 on a 46g tank with less surface area I am wondering if this is the problem. that I have too much flow for my surface area being so small? So my tank fills faster because it is smaller and my overflow box is not draining fast enough. I dont understand why my overflow box just does not drain faster? I really would hate to have to restrict the flow on my return pump? Help!!!
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[fijiwigi]

I added a ball-valve and closed it just a hair. Now it doesn't seem to be an issue. This restricts the flow a bit. Later I will have to fix it so that it flows back into the return pump zone. its crazy how little things make such a difference.

[mandown123]

good idea with the plastic chicken wire around the overflow. twice already ive woken up to my clownfish (the ...slower... of the pair) in the back box

where did u pick that stuff up?

[melosu58]

I had to put a ball valve on mine also fijiwigi. That was probably the easiest solution.

[Ziggy953]

For maximum flow you will want to use 1" PVC pipe. 1" pipe allows for 600gph drain flow. Using smaller pipe will restrict the amount of water that can flow out of your tank. There is nothing wrong with using the Mag7 in your tank. I think by upping the drain lines to 1" PVC you will eliminate the need for the ball valve.

Also on the 90 that you have going under your stand make sure that it is sloped down slightly (the horizontal part) if it is sloped up at all this will greatly reduce the amount of flow.

[fijiwigi]

With 1" there would be more flow than 3/4" creating a bigger problem I have more flow now with the 3/4" than my overflow can handle. I am using vinyl tubing with no elbows so it is just straight flow which really sped things up over the 1/2" hard PVC with elbows that I had. I really didn't want to restrict the flow with a ball-valve but don't see another option. Ziggy953 I am not quite understanding the part about the the drain sloping down. once the water gets into the overflow box it drains fast into the drain. The problem appears to be that the u-tube is not sucking in the water fast enough to keep up with the amount of water flowing into my tank via the 3/4" return line. The part I don't understand is the Overflow is rated to handle more flow than what I have.

[mandown123]

get a bigger U tube - no?

[fijiwigi]

Originally Posted by mandown123

get a bigger U tube - no?

I thought all u-tubes were the same size? Where exactly do you buy u-tubes of different sizes?

[cccapt]

It is rated to handle 700 gph on a 75g tank with a mag7 and 500gph on a 55g tank with a mag5.

That doesn't make sense. The diameter of the drain line doesn't change, so how can the amount of water it can drain change? What is the diameter of the u-tube and what size is the actual drain line. FYI, a 3/4" line will only drain about 300 gph.
Check out this drain/overflow calculator.

[Skyrmir]

It looks like you have room there to just add a second U tube. That should handle the extra flow easily enough. That's actually how they make the higher flow boxes. They double the U tubes and put on a larger drain pipe.

The other option would be one of these:
CPR Overflow Boxes
The cpr-90 easily handle the flow from my mag 7 at a 2 foot head height. The only trick was putting a T in the drain pipe just before it hit the sump. One side going straight down, the other going off to the side a few inches, then going down.