Pond Boss Forums AERATION Systems questions Membrane diffusers blowing large bubbles...

I use membrane diffusers in my recirculating tanks and my moving bed biofilters. I had one a week ago start blowing big bubbles and replaced it. It looked quite old and the rubber membrane looked old and warped on one side.

However I'm having the same issues with a couple other ones that are not that old, one in moving bed filter and one in a fish tank. I had a fairly new on do this in a fish tank at one of the high schools and replaced it. I couldn't find anything noticeable wrong with it and ended up using it in another system with no issues.

Anybody have these things wear out. I do run them 24/7 so they do get a work out.

I'm not using an excessive amount of air so they aren't blowing out of their seals.

Are you running them at a low CFM the only thing that comes to mind is that without enough drive pressure the bubbles are merging on the membrane and then breaking the bond as a film of algae or anything forms on the membrane this could also help move the bubbles together.

This is just me thinking of how dew drops merge together and then finally form a drop of water and from what I have seen on my faceport during a dive small bubbles will form near/around the corners of it till enough of them merge together and then "roll off" over the face port flange.

Only thing I can think of is to burp the system or perhaps to pull and clean the diffusers.

Just my 2 cents as I'm still learning just ideas based off life experiences in a different setting.

Thanks for the comments. I'll try your suggestions.

Yes pretty low cfm. 1.4 cfm (40 lpm) to three diffusers.

There is no algae in these indoor tanks due to the low light conditions but there is scum that builds up on the diffusers.

By Jove Diver Cody I think you're on to something! I took a broom and rubbed if over the surface the best I could and the performance increased quite a bit although there are still some large bubbles. I'm going to either burp next and see what happens and/or remove it and scrub it with a scrub bud too.

Membrane diffusers do need periodic cleaning despite what sellers say in their promos. Numerous ways membranes can clog depending on type of water body where they are working. Periodic cleaning or scrubbing off a membrane diffuser is almost always beneficial for performance.

All the membrane diffusers I have seen on the market require .5 cfm, minimum each to operate.....with a max of 5 cfm. Too low on the flow and as divercody mentioned, bubbles do not break tension properly, coagulate into large bubbles, nor do they flow from all membrane cuts....too high of a flow, and you blow the diffuser out of the retainer ring, or stretch it out...

Regular cleaning and flexing is a must to keep them efficient

Makes sense guys!

I agree with the regular annual cleaning. I use a scrub pad. A clients ponds weren't getting the diffuser "boil" that they normally had. A scrubbing and a burp or two brought the boil back to normal. Those diffusers weren't cleaned in 3 years.

Makes sense. Partially plugged diffuser + constant air flow + rising supply pressure = big bubbles and possibly big holes. Something has to give somewhere.

I wonder if you could just record your baseline operating pressure and monitor that. If you see the supply pressure creeping up, time to clean the diffuser?

Now Bill that makes too much sense! LOL

That's why we recommend having a low pressure gauge on your compressor manifold. (0-30 psi)

You'll see approximately .5 psi for every foot of water depth over the diffuser, and I've seen pressures increase 5 psi from Spring to Fall on the same diffuser just due to growth.

Cecil, if you could put shutoff valves to each diffuser, by closing off two then stopping and starting the pump, the extra cfm would tend to blow the holes out better than just cycling the pump attached to all three. Or a cheaper way, just pull the hose and hook up each diffuser one at a time directly to the pump. Pull the hose off to let the diffuser collapse, attach the hose till air comes out, repeat about four or five times.

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I do have a valve for each airline to the diffusers as I have to adjust the flow to each from one compressor. I concentrated all the flow briefly to one diffuser but it seems brushing the diffusers with a broom helped the most. It also really freaked the fish out.

When I move the fish to two high schools from one tank I will drain it down and scrub the diffuser good. Right now it's impossible to reach by hand.

I was amazed at how crusted over my three diffusers were after running just a few months. Two were not so bad, but the third was so crusted over air was only coming out of about a third of the surface area.

In my case I was scuba diving in the pond doing some other maintenance stuff. Kind of as an afterthought, still had some air left so decided to check the diffusers. Glad I did. After pretty aggressive scraping, rubbing and tapping with my hands on the running diffusers, air flow was visually better. Significantly better on the worst crusted diffuser.

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Scrubbing the membrane duffuser made all the difference. Thank you all for the help. Why it did not occur to me was:

1. I didn't think a film could adhere and grow enough to block flow severely enough -- while air is coming out.

2. It didn't occur to me the air would coalesce into large bubbles by the film blocking other areas of the membrane. Makes perfect sense now!

3.) I do have an old one here that is bulged on one side so they do eventually wear out. I also had a membrane blow out on one side on a brand new one. In that case it was apparently because the the frame wasn't tight enough. The air flow was not that high.

All I can say is bacteria adheres to hostile surfaces a lot better than I thought! One text I have says it's important to rough up a surface on an RBC for adhesion of the bacteria. Not so sure about that now.

Snrub, I believe some SCUBA is in the stars for me too, unless I want to pull the diffusers in the big pond up ever year. I need to do something with my certification someday anyway, and I'd like to see those hawg perch and bluegills under water!

Glad it worked out for you.

Thanks for the ideas!

Good chance to brush up on your scuba skills Cecil. Good luck on seeing the big fish. They can see you and know where you are at long before you see them. All I have ever seen in my pond is up to about 6" ones. The larger fish seem to be very wary. But I'll have to say every time I've been it was to do other work and not specifically to find fish. If a person swims about in a pond they likely will never see a fish. You have to sit very still and be patient. The fish get curious of what in in their area and will come around and investigate.

Done regularly the fish will become accustomed to a diver and if fed under water can become pets. Local dive club in a local lake had a cove they used for training. They took hot dogs with them each time and got the CC and a few other fish hooked on hot dogs. So the fish would come up to about any diver and see it there were any handouts. If not they moved on.

In really low visibility water, the only way to ever see fish is lay on the bottom at the appropriate depth, ideally put something in front of your mask on the bottom that is light colored (like your hands) to give your eyes something to adjust to, then just wait and try not to move anything, even your eyes. Kind of go into a trance. The fish will start coming around in a couple of minutes. If you happen to park on or near a BG nest, they will show up quickly and be in your face. Had about a 5" one dang near draw blood from my ear because he did not like me being in his area.

I was diving in a reasonably clear (maybe 12' vis) lake many years ago. My buddy and I parked in some dead trees at 5 or 6' depth and just sat there. Saw a few fish come up and check us out. Then all of the sudden fish started streaming by. Odd..... then two divers came swimming by. later I talked to the two divers that swam by. they swore there was not a fish in the lake. They never saw a single one the whole dive. The reason they never saw fish is because they never stopped swimming. Fish can see us well before we can see them. They stay just out of sight.

Clear water where I'm at now (80-100' visibility)is a whole nuther situation. Totally different than lake or pond water. See fish all the time easily. Not so in murky water. You have to work at seeing fish. I have yet to see a catfish in my pond while under water.

Thanks for sharing.


My trophy pond is quite clear. Visibilty is all the way to max depth of the pond which is 9 feet if I don't use the Aquashade. But even with a good dose of aquashade I can still see quite far.

If only there were a product out there that could make retrieving your membrane diffusers up off the bottom for yearly cleaning much easier. And without the aid of a float on the water surface?

http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=326883

Just off the top of my head, what if you were to attach an inflatable bladder of some sort to the diffuser station...run a separate airline with a check valve down to the bladder, and connect the other end via valve to your compressor manifold.

When aerating, leave valve to bladder closed. When it's time to clean the diffusers, shut off air to the membranes and open air to the bladder.

Inflate it, and let it float the diffusers to the top? The weighted airline, combined with weight needed to sink the diffusers might present a problem, but with minimal added weight, (just enough to sink the diffusers) maybe it would work?

Ok, keep in mind you asked for ideas. I haven't tried this. The idea is to take about a 3 foot length of maybe 1/4 inch nylon rope and attach one end to each side of the diffuser towards one end of the diffuser. Tie a float half way along the line. This should always keep the rope loop suspended above the diffuser and off the bottom. When you want to retrieve the diffuser, take a grappling hook on the end of a small rope and snag the suspended loop. Hopefully, by tying the loop at one end of the diffuser you will minimize the impact on the vertical water column the diffuser is producing.