A Blueline 100. Not happy with it. A killer on power bug time. Will be changing it.

It's pretty unlikely that you have something like a pinhole in the side of a pipe, you just don't have enough pressure to rupture PVC. If you have a hole it will be somewhere at the edge of a fitting where the glue has a space in it. This space could theoretically allow air to be sucked in by the movement of the water through the pipe like the venturi on your skimmer works.

In practice this is pretty unusual in a return line, the back pressure would be more likely to force water out of the hole than draw air in. Due to the rise in your system I imagine you have a check valve on there that will keep the pipe full with the pump shut down. Turn off the pump and look for leaks either in the plumbing or around the pump volute.

The answer to your question is cavitation

I had the same problem with a Iwaki return pump on my old 330G reeftank

Just put a ball valve or gate valve on the output side and throttle back the output a bit


bubbles gone :biggrin:

Not necessarily cavitation but something similar. Could you describe what the plumbing looks like from the sump to the pump? Likely this part of the plumbing has too much restriction which results in a low pressure situation. If the pressure is low enough dissolved oxygen will actually be liberated from the water, a very common problem that most never figure out and usually blame it on a pin hole which is actually pretty ridiculous when you think about it.

A quick fix is restricting the output flow of the pump as already mentioned, this will in turn increased the pump intake pressure. A better fix is to plumb the pump properly.

Restricting the output of the pump will reduce the cavitating, however if this system has been up and running for some time then this should not be the issue, and it sounds more like a restriction on the input side.

Well I did all that was mentioned and then hubby did the same. The pump will work fine, then suddenly have little to no flow, and then the bubbles with low to almost no flow. It has worked fine for abut five weeks since it was installed, and now for no reason at all it seems, it is doing this... I removed it and cleaned it but there was nothing in it at all.

It was not too bad at lights on but now it hardly flows at all and I have billions of little bubbles then none... then bubbles etc... etc...

We paid $600 for this pump and will be buying a different brand sooner then I would like. Prior to this one, we had an Iwaki and the same thing happened after about a month.

I'd be taking it back to whereever you bought it and raise a fuss. See if it's maybe common with that brand?? Sorry about the luck

I have a serious desire to come out there at some point and look at your sump. If this is the second pump that's done this, then something is up. Nobody is this unlucky (trust me, I know a thing or two about unlucky :p ) Something is not right about something, but without a detailed look I can't really speculate based on your descriptions (sorry, what I mean is, I can't visualize the setup)..

The first pump was not nearly strong enough to run the system. The LFS guy took a chance in selling the substandard pump for our needs, but he did the same for our skimmer as well. He ordered the new pump and we paid extra for it. When I brought the two week old skimmer back, I lost $100 on it and only got store credit.

24storm has been to my house a couple of times and he said everything was awesome. I do think it is bad luck to be honest.

I trust Keith's judgment but I still think there has got to be something else at work here. A pump can't fail because it's not strong enough ... if it's not strong enough to lift the water, you'll just have poor flow. However, if there is restriction on the intake side, then indeed, you are pushing the pump beyond it's limits and risking failure. In short, pumps push, they don't suck. Two pump failures in this short of timeframe may just be coincidence but it's now the point where I'm skeptical. If you have a third pump fail on you then I'll know it's not coincidence.

Who did the actual plumbing on your system, may I ask?