Please help understanding overflow box on my tank - pics

[krashpd]

This is a 90 gallon corner acrylic that I bought used. It is a reef ready tank that has a built in overflow but I don't completely understand the way it was designed. The overflow is in the very back and takes up the corner. It has three compartments. The main in the very back has two overflow tubs of different material and different size drain holes. On each side of the overflow box is another compartment that holds bioballs. These two bioball compartments have slits in the bottom for return water to the tank. The built in overflow does not so it seems like water that goes to the bottom of that box will just sit there with no movement at all. Here are the pics:

Overall picture of tank without the canopy

Top of tank.

Overflow box with two drain pipes.

Another View.

This first drain is about 1 inch and about halfway down it becomes a 1/2 inch opening.

This second drain stays about 1 inch all the way down through the bulkhead and out to the sump.

Here is the side compartment where the bioballs were.

Here is where both drains exit from the bottom of the tank.
I don't understand why the two overflow drains would be different sizes. The original owner had the first drain just capped off below the tank so that water would just sit in the pipe and never move. I am also concerned that the water in the bottom of the overflow box will not move either and maybe become toxic. I was planning on connecting both tubes to my sump but does that sound right to everyone else? Thanks for the help on this. I really want my tank set up right the first time so I am taking my time to get all of the worked out.
Thanks,
Krash

 

[kimc]

just a little bump....

 

[sinaloa213]

one of them pipes are to return the water and the other is for the water coming down into the sump

 

[krashpd]

There are actually two holes in the main part of the tank with one inch bulkheads for the return of water from the sump. Would they really have three returns? the manifold I have is just made to pump the water back through the bulkheads with loc-lines in the main tank area.
Thanks,
Krash

 

[dogstar]

Can not explain why both drains are different, IMO just build new stand pipes ( durso style, cheap, quite and easy...) Its OK to run both drains to the sump....Carefull with those returns not flooding the sump if power fails...

 

[acrylic51]

Yeah build new Durso's as suggested....super easy and cheap and adjustable to quiet things up as well.....

 

[krashpd]

Thanks for the help. I'll have to research the Durso's because I've never seen them before.
Also, I thought pumps would have a one way valve so that water couldn't drain back through them if there was a power outtage. I'll have to fix that as well before I get to putting water in the tank.
Thanks again for the help.
krash

 

[acrylic51]

Yeah check out dursostandpipes dot come really easy to make......You can utilize check valves on your pumps on the output side of the pump, but they aren't 100% at working all the time, but along with a check valve and drilling your return lines if they are submerged underwater with a anti syphon hole should prevent some of the water back syphon to your sump......
There's more to preventing water back syphon and to prevent sump floods then most people will tell you.....You can use all the above methods as I Suggested, but run you sump to high and don't properly plan for the amount of back flow you'll get if the system were shut off you'll have water on the floor......There are ways to double check your system to make sure it won't back syphon to much water to the sump and to make your your sump will handle everything....

 

[krashpd]

Thanks for the info Acrylic. I got on that website and they look very easy to make. So I guess I should just replace both pipes with the Durso's and I would have plenty of flow to the sump. I need to order new bulkheads I think since I am replacing much of the plumbing that came with the tank.
I'll start to look into how to keep the water from draining back into the sump through the returns. That last thing I need is 90 gallons of water on the floor and a huge livestock loss.
Thanks,
Krash

 

[acrylic51]

Yeah I'd replace the bulkheads or at least the rubber seals......Both are relatively inexpensive........You can use check valves, but they are know to fail, but is sorta a safety, and the other option is to drill your return lines if they are submerged under water. You would drill your return line below the water surface with a small hole, that way if the power would go out, it would drain to that point and break the syphon.......The other way to go is when you set up your system to play with the highest water level you can run in your sump, and shut the power off and see how far the system back syphons to the sump......It takes a while to do, but this should be done no matter what methods you employ........Pic of a see through rebuildable double union check valve....