This is the best I could do when doing some googling. HTH's Troy
EDIT---I think this has to be related to too little air or too much air.
I know you have the other modification so I guess change the settings a little. I wish I knew for sure.
Overflow & Standpipe
by richard durso
My Oceanic 180 gallon tank has two overflow boxes, one in each back corner. Each overflow area measures 8 inches deep, by 11 inches wide, by 24 inches high (20 x 28 x 60 cm). Before I made this modification, the stand pipe that came with the tank was a tube with a million holes in it. This allowed the water to flow into the pipe quickly. However, this also meant that the water level in the overflow chambers was very low -- about 3 inches deep.
With such a low water level, water entering the overflow chamber had about a 20 inch drop! This sounded like Niagara Falls. (At the time about 1,500 gallons per hour enter the overflow chambers) Secondly, each chamber made a gargling noise -- sounded like a toilet flushing 24 hours a day. It was so loud my wife could not sleep. I had to fix it fast!
A solution was suggested to me by Mark Lanett -- use a solid stand pipe with a submerged intake. This solution solved all my problems:Little to no water fall.
Whisper quiet, no splashing or gurgling.
Each chamber becomes a refugium.
Chambers will not drain in a power outage.
Pipe is self priming.
There are a few details that need to be brought up and are important if you plan on using this modification. I'll start at the bottom of the pipe at the bulkhead:
My tank has a 1 inch bulkhead on the bottom glass where the water drains out. For this size hole, I recommend you use 1 ¼ inch or 1 ½ inch diameter PVC for the stand pipe. This is very important, the stand pipe needs to be larger than the bulkhead to work correctly. I used 1 ¼ pipe because I had some extra PVC from another project and this is what I recommend. I get a lot of e-mail questions on why this is. Honestly, I'm not sure. If you use 1 inch pipe on a 1 inch bulkhead you get poor results. Take my word on it and use larger pipe.
First fitting is a 1 inch threaded male adapter which screws into the bulkhead. Be sure to use plumbers tape on the threads, you want this to be a water tight seal. Next, I convert the 1 inch pipe to a 1 ¼ inch pipe using a reducer bushing.(There is a small section of 1 inch PVC pipe linking these two parts, use plumbers tape on both ends) Then the stand pipe is inserted. The PVC pipe is Schedule 26 type pipe which is thinner, lighter and drains better than schedule 40 pipe. I used PVC cement for this connection to keep it water tight. At the top of the stand pipe is a 1 ¼ Tee fitting. This is attached to the stand pipe with plumbers tape only. I wrapped it around 6 times to get a good tight seal. By not using PVC cement, you can later cut the PVC pipe if you find the water level is to high. A special elbow connector called a "street-ell" is then inserted and pointed directly downwards. This is the water intake, it will always be submerged. Since it is submerged, it can not suck in air.
Note: A street-ell allows the ell to be inserted directly into the Tee fitting without requiring a separate small PVC pipe length to connect the elbow and tee together. A standard PVC Elbow can be used but may not be as compact as the street-ell. To fit into small AGA style overflows, just trim ½ inch off the street ell connector.
I used PVC cement to connect the Street-Ell to the Tee. You might want to use plumbers tape, this connection does not need to be water tight. On the top part of the Tee fitting is a small section of PVC pipe and then an End-Cap fitting. The End-Cap is held on with plumbers tape. A very small, as small as I could make it (thickness of a toothpick), hole is drilled in the top of the End-Cap fitting. This allows some air to enter into the stand pipe.
I would suggest starting with a 1/16 inch drill bit for the air hole in the End-Cap. If you find the water level in the chamber fluctuates quickly then the standpipe needs to suck in more air. Try a 5/64 inch drill bit to make the hole slightly larger.
The hole on the top of the stand pipe (in the End-Cap) is very important. Without the hole, a full siphon will be created and water will be sucked out of the overflow chamber to fast. The water level will drop below the intake and you will get a terrible air sucking noise. If you drill a hole and the water level still drops to far (making a sucking noise) then the hole is to small. Just make it slightly larger (see above) and the water level will raise. If you make the hole to large then the water level will be to high. (It should not overflow the tank as it will not get that high, but keep an eye on it). If the water level is to high this can be fixed easily. Seal the hole with aquarium safe silicone and use a toothpick to make a small hole in the silicone. If this turns out to be to small, remove some silicone with a smaller drill-bit or some other tiny sharp object. No silicone handy? You can try some old well chewed bubble gum to reduce the air hole size for testing If you really mess up, then get a new End-Cap (they are cheap).
You want the water level in the overflow chamber to be about 2 inches lower than the rest of the tank. This provides for gas exchange and prevents a slime film from building up on the water surface. If you designed it correctly, the water level in the overflow chamber will be a few inches lower than the rest of the tank, and the water level will be at the middle of the Street-Ell fitting as pictured above. If the water level is slightly higher, no big deal. As long as the overall water level in the chamber is a few inches lower than the rest of the tank its good enough.
9 - Toothpick sized hole drilled into End-Cap (8) or use an air-valve.
8 - End-Cap.
7 - Small PVC pipe used to connect End-Cap to Tee Fitting.
6 - Street-Ell. This connects to the Tee fitting. This is the water intake for the stand pipe. The water level should be somewhere around middle of the Steel-Ell if constructed correctly. If slightly higher it will not be a problem. If water level is at the opening of the Steet-Ell you will get a sucking noise. Make hole in End-Cap (9) larger. If you have trouble getting it all to fit in the overflow box, a ¾ elbow should fit snug directly in the 1" tee opening.
5 - Tee fitting. This connects the End-Cap assembly and Intake (Street-Ell) to the stand pipe itself. You'll want to connect the Tee to the standpipe using plumbers tape. This will allow you to remove the Tee fitting if you need to make the stand pipe shorter.
4 - Stand pipe. This should be wider than the bulkhead opening. For a 1 inch bulkhead use a 1 ¼ or 1 ½ diameter PVC pipe. All other fittings used are based on the diameter of this PVC pipe needed.
3 - Reducer Bushing. This connects the stand pipe to the threaded male adapter. If you use 1 ½ inch diameter PVC pipe and you use a 1 inch threaded male adapter, then you need a 1 ½ to 1 inch reducer bushing. (A small section of PVC pipe may be needed to link this to the male adapter below)
2 - Threaded male adapter. This attaches the entire stand pipe assembly to the bulkhead. If your bulkhead is not threaded, then this is not needed. The reducer bushing could be attached directly to the bulkhead. Be sure to use plumbers tape on the threads before screwing into bulkhead. This will help keep a water tight seal.
1 - Bulkhead. This is the opening in the bottom of your overflow chamber where water drains to the sump.
Then we can all sit back and have a cold one....
