Something that Towerklean users should watch for when doing a visual inspection of the system (you DO visually inspect daily we hope!) is air bubbles in the reaction column. There should be no bubbles on a normally functioning Towerklean system, other than right after startup.
Bubbles will carry media out the top of the column with them. The flakes of media get a free ride out of the system and into your tank. Eventually there will be enough media loss to affect system performance. Therefore; bubbles = bad.
What to do if you are experiencing bubbles? Check everything on the suction side of the pump, fittings, etc. Check the lid seal on the strainer basket, along with the gasket between the Basket and the pump.
You may have to watch closely to spot the bubbles! But if they are there you could have trouble. HM.
A strainer attached under the return line to the tank is about all we would recommend. And some have done this. It also helps during initial startup of a new system, because there is always some dust and fines that get flushed out into the reservoir tank.
If it were an inline strainer, and media was in fact escaping, the flow would eventually be effected and the treatment capability would suffer. However with a strainer (cloth or otherwise) hanging below the return pipe in the reservoir, even if it gets full of media we still will have flow. HM.