Dual drains for 90Gal


Reefing newb
I'm new to the hobby and am setting up a 90G DT with a 55G sump in the basement below. The DT was "Reef Ready" for two bulkheads in the bottom of the overflow chamber. One 1" and one 3/4". I'm using both for drains to the sump. The 3/4" is running to a bulkhead in the sidewall of the sump feeding the "fuge" section. The 1" is running to the skimmer section and entering from above (no bulkhead). Both lines are valved. I'm using the "Durso Design" stand pipes in the overflow chamber. The 1" bulkhead has a 1 1/4" thin wall pipe and the 3/4" bulkhead has a 1" thin wall pipe. I've finished the plumbing and have filled the system with fresh water for "testing'. The good thing is I have no leaks. The troubling thing is I'm dragging a lot of air from the overflow chamber to the sump through both drain lines. I have experimented with different stand pipe air vents and heights, etc with no success. I have run the system and calculated that I'm getting 625 GPH of water back to the display tank with both drain valves open. That flow seems to be on the low side of what is reccomended (from what I read???) Here is what I think I see happening and need your advice on. When the system pump is pumping full bore back to the DT and I'm getting the 625 GPH the overflow chamber baffle can't handle that flow rate through the oval shaped holes. (There are two rows of holes, one near the top and one near the bottom). There is some water breaching the top of the overflow baffle as well. Even though there is some addidtional water flowing over the baffle top the standpipes are still starving for water and therefore "dragging" air to the sump. If my contention is correct then it seems I would have but two options.The first would be to add more holes in the factory overflow baffle or to valve back everything, drains and return. If I valve back I don't believe I'll get the recommened flow through the system. What am I missing? I can post photos if needed. Help Please! Curt
Why are you using both the holes for drains? The big one is supposed to be the drain, and the small one is supposed to be for the return line.
I've chosen to use both so I would have the option of more flow through the system if that need arose. As I have explained I can't get the minimum flow now without issues, what would I do with just one drain?
I'm not sure. I have a 90 gallon that is plumbed with two holes -- one for the drain, one for the return. I have a ton of flow in my tank.

One drain of that size can only drain around 600 gallons per hour. You are trying to double that by using both holes as drains? My guess is the overflow tower is not large enough to accomodate the amount of water returned from the pump if you are trying to drain from the two holes. It was built for only one drain. Which is why you have water coming over the top of it when you turn the pump on full-strength.

Almost no one is able to run their return pumps at full strength without using a ball-valve or gate-valve to dial it down. That's part of making sure your system is in equilibrium.

It's also impossible to achieve enough flow for a reef tank using the return/drain system alone. You have to either use a closed-loop system or powerheads for additional flow. If you are trying to achieve 100% of the flow you need just from the overflow, then your basic premise was mistaken. Buy some powerheads.

Maybe I am misunderstanding your question, but I really think you are making this a lot harder than it needs to be. Everyone else with that type of tank doesn't seem to have problems when they use the two holes as they are intended. You can't count on the return from your sump to provide you with the flow you need for your tank. It's not supposed to provide that much flow.
The drain can only handle 600gph and even that is not realistic.350-450gph is more accurate.Anymore than that just causes the pipes to gurgle and burp.Of course water is going to go over the top of the overflows,they were never design to have two drains in one chamber.You are confusing flow and turnover.You don't need a high turnover for the sump and flow can be added by circulation pumps/powerheads or a close loop system.The overflows are design to bring water to the sump and back,they ae not enough alone for flow in the display.
To Reeffreak & bifferwine: Thanks for the replies. It does indeed sound like I don't understand what "Flow" is. Are you saying that flow is nothing more than water movement and not necessarily going through the filter (sump)? If that is true then what "turnover" rate do I need for FOWLR and how do I measure flow? Do I just use an advertised GPH for the given unit(s) that I may purchase? I may get this thing going yet!!!
Do I just use an advertised GPH for the given unit(s) that I may purchase? I may get this thing going yet!!!

Exactly! Flow is water movement. Even if it's via a powerhead which is isolated in the tank, away from the sump. Powerheads are rated to move a certain amount of gallons per hour (gph). If you have four powerheads, you add their gph together to get the "flow" in your tank. So if you have four powerheads that each push 200 gallons per hour, you have 800 gallons per hour total in your tank.

The return from your sump is going to contribute to that, but not be the entire amount.

To get your sump dialed in, you will need to adjust your return pump (using a ball or gate valve) until neither the sump nor the tank overflows. And that's the flow from the return that you will be stuck with. Remember, with an overflow, you can only drain as fast as the pump is returning the water, and you are looking at 600 gph maximum through the drain.
Exactly,add up all the pumps/powerhead gph will give you your flow.You don't need as much flow in a FOWLR then with a reef system.If you have a mass market aquarium with a single overflow use 350gph as how much water is passing through the sump and back to the display + add up all the powerheads/circulation pumps.

I personally would just use the single drain and add powerheads for as much flow you want.The Koralias are pretty inexpensive and work well.Two Koralia Evo model 4's would be good.This is not rule but only a guideline with many exception I stole from wiki-total gallonage x10 fish,x 20 soft,x 30 for LPS,x 40 for SPS.Your gallonage is 145 total and I would go with 2800-3000gph which would put you at x20 rate.
.This is not rule but only a guideline with many exception I stole from wiki-total gallonage x10 fish said:
OK, Powerheads are my answer but are there not some guidelines for a turnover rate for a tank of a certain type & size? Now what the heck are those above. Please explain. Remember, I'm brand new at this LOL
The turn over rates are lower. I have a 90gallon DT with a turnover rate of 7.5 if im lucky. Running Mag 9 pump with head of 4ft which drops the flow down to like 700gph, which is what my overflow is rated at. I get burps every now and then but not much.

Most of what you read online from sites recommend 10times turnover through the sump. You need to have an overflow that can handle that mine does not so I have less.
Your total gallonage is 145g.(90g display/55g. sump).

x10=1450gph for a fish only system
x20=2900gph for a soft coral tank
x30=4300gph for Large Polyp Stony(LPS) corals
x40=6000gph for Small Polyp Stony(SPS) corals.

Like I said earlier it is only a guideline.There are many exception to the rule.How much live rock is use and your own preference to name a few.I think 1450gph is a little low because one Koralia evo 4 puts out 1400gph and I think two Ke4's would be better is why I suggested x20.
another good tip instead of just cutting back flow from your return pump with valve it to divert the flow back to your sump so your not putting your pump in a bind. just make a tee after your pump with a valve on both side of it, on to the dt and one to the sump. leave the one to the dt wide open then slowly open the one to your sump to divert the flow back to your sump thus less going to your dt.