Gurgling noise in overflow box (the air intake hole of pipe # 2) -diagram included

[MarshallPlacid]

Hello fellow hobbyists.

I need some help and I hope anybody here can help me.

It is the very annoying LOUD gurgling noise problem with my overflow filtration system.

Tank specs:
187 gallons with one overflow into a sump with a 5 box type filter (a filter system with 5 separate compartments of water) with 2 drainage pipes
Pump is 900 GPH Einheim (spelling) pumping back out from one hose/pipe system.

FINDINGS: the gurgling noise is coming out of the air intake HOLE of pipe # 2 (see diagram below).

I attached a picture of the current configuration and some solutions I already tried including:

1- Attaching air intake hose (3 ft) into air intake hole for pipe # 2. Gurgling noise stops, but pipe 1 stops working, so the sump only has 1 pipe draining instead of 2 pipes (which is a requirement).
2- Lowering the ball valve so that only a little water flows out from the sump back into the tank. Gurgling noise stops. Both pipes 1 and 2 works and drains water. BUT, the pump is overtaxed because backward pressue is being forced back into the pump because the ball valve is almost 90% closed to only allow a little water back into the tank. This broke my first pump after 2 or 3 days. So, adjusting the ball valve does not solve the problem. It will only break the pump after a few days. Also, the GPH flowrate will be so low as to make the fish tank become unhealthy. I need at least a 4 or 5 times turnover rate for the fish tank filtration system.

What other solutions are there to this annoying problem?

I have tried asking my local saltwater fish store for help and the fish tank seller for help. No one has been able to help me. The manager of the store is on holiday, so I have to wait 2 weeks. I want to solve this problem now, with the help of this forum and the participants.

I sincerely appreciate any comments, help, or tips you can give me.

[Reefing Madness]

Critter climb into the pipe? Tough to find out, but I think you need to. You won't damage the pump like you think, its ok to control flow on the return line, but you will blow up the pump if you restrict in inlet. And I'm confused, I don't see the pipes tied together anywhere, why would one hinder flow in the other?

[FoMoCo Master Tech]

What size pump? What is the size of the drains? Maybe adding an elbow to the end of the drain pipe to try and slow the water down. I assume its all PCV plumbing.

[Original Fin]

Are these internal overflows we're talking about? (drain pipes would exit through the bottom of the tank)

How long have you had this system and has this gurgling noise been present since the beginning?

The main thing that strikes me is this...

You said that when you insert a breather tube in pipe #2, that pipe #1 stops to flow. This is odd to me, and I can't come up with a reason that would happen except that there could be a mismatch in height between the two overflow weirs. This is just a guess, but it could be that when you use a breather tube on #1, it increases flow on that end, and maybe that's just enough to keep the level from rising over the wier on the other end. Have you checked for level on the tank?

Are overflow pipes #1 and #2 symetrical and of equal length with the same dia tubing/pipe? They should be...if not, one will be able to flow at a higher rate than the other. This can be compensated for by adding tuning valves to the overflow pipes themselves.
What size is the overflow tubing?
Gurgling is always present to some degree with this type of overflow. You can tune the gurgling down by using creative plumbing like you have tried to do, but there will always be some noise. Smaller pipe diameters used with more powerful return pumps increases this tendency. Large diameter tubing and less powerful return pumps reduces it.

Have you looked into standpipe silencers like the Stockman, Durso, and Hoffer Gurglebuster?

[MarshallPlacid]

FoMoCo Master Tech - The pump is a 900 GPH pump.

Reefing Madness - no critters. As I just started teh tank a week ago. I want to fine tune the tank before I put in animals.


Original Fin - Internal overflow box.

when I stick a long air intake pipe/hose into Pipe # 2's air intake hole, this lowers the overflow water level so that Pipe #1 (which is a little higher than Pipe # 2) has no water going into it (the water level is below Pipe # 1's water intake hole).

I took a look at the durso and stockman mods and they may help, but I was hoping for some other solutions first.

The elbow that you guys suggested may do the trick.

[Original Fin]

In that case, it sounds like either the tank is not level, or the two overflow weirs were mismatched when the tank was assembled. If levelling the tank is not an option, you should be able to add a tuning valve to overflow pipe #2, and gradually close it until you get even flow between the two. It shouldn't take much, and that's something you should be able to retrofit without shutting things down. Put a cap on the one you intend to work on, and let the other one do all the work till it's done.

In this application, I would use a gate valve over the typical ball valve. They are much easier to adjust and won't put nearly as much strain on the bulkhead and botton glass when you are using it. PVC gate valves (Looks like a garden faucet handle) have a reputation of developing small/slow leaks, which is explains the prefference for ball valves (Has a T handle) in this hobby, but as long as it's situated over the sump and has somewhere to leak back into the system, you have nothing to worry about but the occasional salt creep cleaning. This is better IMO than risking blowing out the bottom panel of the tank when you crank down on a ball valve. You have to exert a lot of pressure on ball valves, so effective strain relief for the attached plumbing is critical, especially if it leads to a bulkhead.

Of course, that doesn't adress the gurgling issue, but at least it would fix the problem with uneven sump levels.