Hi, I have a pump but I'm not sure what output it has but I added an extra line for a bubble wall and it's really not powerfull enough, the main line was for an under gravel filter, so I don't really want to take the pressure away from that as it might hinder the performance. So...I was wondering what size pump do I need...I would like to at lest be able to have 3 lines going at the same time. It is for a 15 gallon aquarium.

Hm, it's sort of hard to determine since it sometimes depends on where you situate your pump in relation to your tank and how long your air hoses are, and blah blah blah...

What you can do is purchase a really powerful one and then buy something to attach to your air hoses that will adjust the air flow. That way, if it's TOO powerful, you'll just turn the knobs on the air flow thingies and let less air in. Try to leave one knob available to let air OUT so that your pump isn't backed up with too much air.

Here's a picture of those air flow thingies: GANG VALVES

Thanks Nenn, good advice. I'll do that.

Hope it works out for you! Sometimes you get a whistling sound if there's a lot of air coming from an extra valve, but it's never been too bad in my experience.