How much can a Megaflow really overflow?

[bullfrog]

Does anybody know how much overflow an AGA Megaflow can handle in real life? AGA says they're supposed to handle 600 gph through the pipes. I have a 180 AGA with dual Megaflows and was thinking of building a closed loop manifold like Anthony Calfo describes here (http://www.advancedaquarist.com/issues/sept2003/short.htm). But instead of running out of the sump, i thought of just pulling the water out of the bottom of the overflows and running a pump level with the top of the tank to feed the closed loop manifold. I've heard that the grills on the Megaflows can't really handle that much flow. So I was thinking of cutting them open like this (http://www.rl180reef.com/180/pages/standpipe/mods/megaflow.htm). I'm still brand new to this, so if I could get some opinions on my idea from people with real life Megaflow experience that would be great.

[NaClFinatic]

Proceed with caution as your limiting factor may be the bulkhead size and not the overflow inlets. Also I would prefer my overflow drain to be oversized and not pushing the limit incase of any buildup in the pipes or some debris slows it down. In that situation you could end up overflowing the tank.

I think that what Calfo shows is not a closed loop but just a differnt way of doing a return. I think a real closed loop takes water directly out of the aquarium and puts it directly back in just to create current. It does not give any chance of flooding unless the connections leak.

[saxman]

Proceed with caution as your limiting factor may be the bulkhead size and not the overflow inlets. Also I would prefer my overflow drain to be oversized and not pushing the limit incase of any buildup in the pipes or some debris slows it down. In that situation you could end up overflowing the tank.

I think that what Calfo shows is not a closed loop but just a differnt way of doing a return. I think a real closed loop takes water directly out of the aquarium and puts it directly back in just to create current. It does not give any chance of flooding unless the connections leak.

agreed...good post.

[bullfrog]

Thanks NaClFinatic. I think you and I are on the same page with the close loop idea, but I might not have written what I was talking about that clearly.
I didn't want to put any more water trhough the bulkheads. I just want to use the area inside the overflows as a place to feed the pump rather than just sticking a feed pipe into the display area of the tank that might suck up slower moving critters. I picture it almost like a giant powerhead using the plastic around the Magaflow as a big intake guard. The pump itself would be over the tank (not in the sump). So I wouldn't place any more demand on the bulkheads, only the overflowing capability of the Megaflows. My idea was to modify Calfo's design so that it is fed directly from the aquarium and make a true closed loop. Here's a simple diagram of what I mean. It's a cutaway view of the aquarium and overflow:

888[]===[]===[]====PUMP
__out__out__out_______[]__
|88888888888888888888[]88|
|88888888888888888|88[]88|
|88888888888888888|88[]88|
|88888888888888888|88[]88|
|88888888888888888|88[]88|
|88888888888888888|88[]88|
|88888888888888888|88[]88|
|88888888888888888|88in88|
|_________________|______|

So the water will flow into the Megaflow, up through the pump, out through the closed loop, and right back into the display. (Of course the closed loop manifold will not be so high above the display. It was just easier to make the picture that way.) I didn't include any of the Megaflow plumbing because it will be entirely seperate from the closed loop plumbing. That's why I was wondering how much overflow the Megaflows can handle rather than how much flow the standpipes or bulkheads can take.

[saxman]

what you could do, is add a "Tee" and a valve on the pump outlet to bleed any excess flow back into the overflow. that way, you can fine tune the amount of water you remove without restricting the pump with little to no impact to your system.

[bullfrog]

That sounds like a great idea. Thanks Greg.

[saxman]

you're welcome! i know the sketch is bad, but you get the idea...

[NaClFinatic]

I still have concernes about the balance of the flow between the closed loop system and the regular drain and return.

Lets start by looking at a normal overflow with a drain and return. In this situation the drain can handle more water than what actually flows into the overflow. No more flows in because only what is pumped back out the return can get over the overflow. The return pump is sized or throttled back to move less water than the overflow can handle. That way it never pumps all the water out of the sump to risk running dry. So this is a nice little balanced system.

Now when you add another pump in the overflow you throw more variables into that balance. By keeping plenty of water flowing into the overflow with the closed loop there is potential to keep the drain also flowing even beyond what the return pump can keep up with. So you set your drain standpipe higher but now if the closed loop pump runs a little strong it coudl lower the level in the megaflow and limit what goes into the drain, then you worry about the return pump running dry. I'm not saying this isn't possible to do. It just seems there are some risks and some careful planning and experimenting will be required. Also remember that even if a balanced is achieved it should account for pump failures or lowered flow as buildup of deposits limit performance.

I think if I was to try this, I would just plug the bulkheads in one overflow and use that one for your closed loop. Use the other one for your regular drain and return. (Well I guess you could return from both.) This means you won't cycle quite the volume through the sump but that might not matter if you dont have too high a bioload.

[bullfrog]

I can see what you're getting at with the sump pump possibly getting more water than it can return to the tank. I was thinking about that myself. But theoretically, in a real closed loop, the level in the overflows or display tank should never change—because the amount of water pulled out of the tank will be exactly the same as what’s being returned to the tank. So even if the pump were to fail you would only need to worry about the amount of water inside the closed loop itself, which should be negligible. So, still theorizing, whether the closed loop pump is running or not, the amount of water flowing down to the sump should still be static. Of course real life is not always the same as theory. :huh: So it’s definitely worth keeping all this stuff in mind when setting it up and testing it out. My main fear was sucking so much water out of the overflows that there wouldn’t be a high enough water level inside the overflows to reach the top of the standpipes and get down to the sump—causing the display tank to overflow because the grills on the overflows just couldn’t keep up with the flow. But Greg's "T" idea seems to solve that problem.

[CarmieJo]

The other thing that you should think about with a closed loop in the sump is that you will loose some flow due to head loss.

[bullfrog]

Yeah, that's one of the reasons I wanted to plumb the pump up above the tank rather than from the sump.

Hey, speaking of head loss and all this stuff, what kind of turnover rate do y'all have in your tanks? And what do you use to create your flow? Do you use closed loops of some sort, powerheads, other?

I've read that for SPS type setups that it's good to shoot for 20x and even 30x turnover or more. Unfortunately the holes that AGA drills for the Megaflows are way too few and too small to handle that kind of flow. So I was just curious as to how other people handle creating the extra flow needed.

[bullfrog]

Oh, what kind of overflows do you have too?

[CarmieJo]

My turnover is 15x but I am getting ready to order powerheads that will double that. I use powerheads in my display along with the return to create flow. I have Megaflows too. I run 550 - 600 gph through my return.

[bullfrog]

Thanks Carmie. That helps with trying to figure out how much water to pull through the sump. I checked out your Tank Journal and it was really cool to see how those bleached coral heads got covered with coraline. It looks great.
By the way, have you heard of the Maxi Jet Mods you can do to make them really flow like crazy? There's a how to video at reefvideos (http://reefvideos.com/).

[CarmieJo]

Thanks Bullfrog. I actually have the MaxiJet mod bookmarked but I am not much of a DIY person. :) I am going to order the Koralia 2 or Tunze 6025, both of which have about 600 gph flow. That will give me 1200 gph in my DT vs. the 500 I have now.

[jwavec]

Not trying to hijack the thread, but this is very interesting stuff. Bullfrog, how big of a pump are you considering for your "closed loop" setup? I am following along on this thread because this is something I may attempt as well. To avoid the possible issues of the overflow not being able to keep up with the extra pump for the closed loop and still drain into your sump effectively, could you not keep the pump above the tank as you have described and inconspicuously place the intake for the closed loop pump into the main display tank somewhere, effectively eliminating the overflow rate concerns?

[bullfrog]

No problem Jwavec. I’m hoping to produce about a 30x turnover rate in my tank. So with a 180 gallon tank I’ll need to shoot for about 5400 gph. I don’t want to totally max out the returns from my sump. So at most I’ll try to push about 500 gph each out of those. That leaves another 4400 gph for the closed loop. I think that would take about a 1/4 horsepower pump to circulate that much water, and I’m guessing a pump that big is going to be pretty noisy. (Does anybody out there run any pumps that big who could say how loud they are?) Another possibility might be to run a couple of smaller pumps in parallel. Then they would only need to push around 2200 gph each.
I’m sure it would be possible to run an inlet to the closed loop pump directly from the display tank. What really worries me about that idea though is, that with the amount of flow getting sucked into it, critters like anemones or cucumbers could easily get pulled into the closed loop and shredded. Even with some sort of guard around the pipe it just seems like a lot of suction, but I’m just guessing since I’ve never actually done it before. I thought taking advantage of the Megaflows would help to diffuse that flow over a much greater area so that the mobile soft bodied critters would have a fighting chance. Plus, the main reasons I want to use a closed loop instead of powerheads is for heat and aesthetics. So if I can avoid an extra pipe sticking down into the display that would be great—though I’m sure there would be creative ways to hide it if the danger to the inhabitants wasn’t an issue.
Maybe somebody else has dealt with a similar inlet vs. animal issue who could offer some advice.