DIY overflow questions...

[mmittlesteadt]

I'm going to make my own overflow box for my 40 gallon breeder. I want as much skimming as possible yet do not want to take up too much real estate in my tank. It will be camouflaged by covering it with something (haven't decided which method yet) so it just looks like an overhanging shelf of rock. No corals will be placed under it so I'm not concerned about shadows from it.

I'm wanting about 400 gph flow. I will be using 1" drains (one full drain, one emergency) and one 1" return. The drains and returns will have gate valves (and no I'm not going to use the valves on the drain lines...I only want them there if I need to do something with the tank that requires me closing them off completely). Of course, I could always use it to dial in the flow if absolutely necessary and with the emergency drain being full open I'm not concerned about gating back the main drain flow a bit if needed.

The elbow of my emergency drain will be turned up, and the main one will have the elbow turned down. I will have the top of my overflow box sit halfway up the trim (from the very top of the tank to the bottom of the trim) as I don't want it right up to the bottom of the lip at the top nor where you could see the water line below the trim. The overflow box will be a five sided box, made of acrylic and fastened to the tank with the bulkheads and gaskets (so I won't be using silicone to attempt to attach it to the glass).

I will also have a 65 gallon sump so I have no worries about flooding (overflowing my sump in the basement).

Now onto my questions...

How deep (top to bottom) should I make my overflow box?

Where should the drain holes sit in relation to the overflow? As near to the bottom that will still allow the main elbow to be turned down with at least a 1/4" space under it?

How wide should it be (front to back)? Obviously I need room to install and remove the elbows as needed, but is there anything else I need to know?

According to the calculator, for me to get 400 gph flow I need the overflow to be a linear minimum of 4" of length. How long should it be? Is there ever too much length for skimming? I see guys with coast to coast overflows so I'm curious if the length is more a matter of choice.

After much reading, I'm not putting teeth in the overflow box (as it cuts down the length a lot) because you get better skimming of a thinner layer of the surface with it smooth. I can always find a way to cover it to not let anything get into it.

Also, how full does the overflow box get with water spilling over the edges? Is it a matter of how fast my drain flows? I don't really want it emptying so fast that I get a lot of splashing into it and would want the main drain to be completely submerged for a full siphon.

I've never used an overflow before, but have been reading tons about them and I have more questions than answers.

Thanks in advance.

 

[mmittlesteadt]

I'm sure it's a "been there, done that"..."it's old news" kind of thing, but I'd really like some ideas. I have some idea having read a billion threads, yet not one really answered my questions to my satisfaction.

 

[RocketEngineer]

The bottom of the overflow box should be 1" below the bottom of the down turned elbow in the box. The top should be 1" or so below the underside of the top of the tank.

The location of the drain holes is determined by the size of the plumbing and should be the first thing you determine. Based on the hole you need for the bulkhead, you need that diameter worth of glass left between the hole and any edge, whether that the top of the tank or another hole. So if you use a 60mm hole saw, you need the center of the hole to be 90mm down from the top of the glass.

Width is determined by access, some folks make it so small you can't get your hands in there but its up to you.

The longer the overflow, the narrower the stream of water going over it which results in the best surface skimming and the least noise. Coast-to-coast is the best at both.

Yes, avoid teeth. Lots of options for covers.

With a wide overflow the water "sticks" to the inside glass so you don't get the splashing noise until you really push a lot of flow through the system. Read about a Bean Animal drain setup as it is the best way of configuring the drains for flow.

HTH,

 

[mmittlesteadt]

Thank you. That helps a lot. I've been reading up on all the various drain methods.

 

[RocketEngineer]

Thank you. That helps a lot. I've been reading up on all the various drain methods.

There are only 3 actual "methods": A single drain pipe using a large pipe and lots of room for air, the Herbie using 2 pipes and Bean Animal using 3 pipes. If you are starting from scratch, Bean Animal is the only way to go.

Lots of names out there confusing things. In reality, they are pretty simple and somewhat related.

 

[fishgate]

You will most likely be using the gate-valves on the drain lines. Your main siphon will probably out-flow your return pump meaning you will get constant flushing and it will be very noisy unless you crank it so it doesn't drain as much. Especially if your target is 400gph. A 1" drain will do much more than that at full siphon.

 

[mmittlesteadt]

You will most likely be using the gate-valves on the drain lines. Your main siphon will probably out-flow your return pump meaning you will get constant flushing and it will be very noisy unless you crank it so it doesn't drain as much. Especially if your target is 400gph. A 1" drain will do much more than that at full siphon.

Yes, I will have a gate valve on my main drain. If I need it to tune the flow that's fine. I'll still have an emergency drain. I'm still just planning everything out anyway so I'm in no rush for anything.