Help with BIORB fish tank

Keldin

It's been a while since I played around with aquariums but the following info should be either completely applicable or close enough that you won't muck anything up.
Small air pumps use a diaphragm that pupm air by being vibrated by an arm with a magnet on the end that sits near an electromagnet which switches polarity to cause the arm to vibrate.
Having said that the part thats most likely causing you problems is the rubber diaphragm which is usually an inch or so in size and screwed to the arm. The rubber becomes brittle with age and tears or tears due to excessive pressure build up (blocked airstone or a clamp on the line to reduce the airflow)
see http://www.aquatics-online.co.uk/Z054164.asp and go to replacement diapragm near the bottom for a pic or typical diaphragm
It's a user replaceable part and probably cheaper than a new pump. You should be able to take the base off and have a look inside to to see if there is any damage. There's usually a very small one way flap valve as well in or near the diaphragm. A good pet shop should/may carry spares or search the web.
If you can't replace this part or something else is the problem any air pump will do the job. You just need to find one that matches the size/output so you're not blasting air through and turning your tank into a scene from a Jaws movie climax or not getting enough air through.
The one way valve that goes inline with the air tubing is there for one reason only:
If you want to position the pump below the level of the water you should have one so that if the pump turns off due to failure or electricity tripping etc then the water doesn't flow back into the pump and out onto the floor ruing your floor, shorting your pump out and killing your fish.

K