Originally Posted by Wasserpest
As you mentioned, this priming pain must be very dependent on the model used. Do you have to do this every time you clean the filter?
Each filter is slightly different, and I have so many. This is why I needed to see the reasoning behind the problems I was having, learning one trick for one filter wasn't sufficient. With 7 canisters I am cleaning one each week, though this is better now that I am prefiltering some of the planted tanks.
With the much older Fluval 303, this was constant problem. Even after a simple cleaning of the filter, with the tubes both full of water, when reconnected, the unit would not start. If I opened the inlet valve first, the air would rise up the inlet, killing the siphon. If I opened the outlet valve first, there was still a trapped bubble in the inlet line, ready to kill the siphon or airlock the motor.
The Classic was often able to clear trapped air without rocking because the setup of the inlet and outlet insures that new water pushes all air out to the top, but understanding the path the air takes makes getting it restarted foolproof.
The Eccos are perhaps immune to this, but you have to disconnect the power and close the taps in the order specified or else the handle gets "fiddly" (as the British say -- I like that term!) do that correctly and it works like a charm -- mess up and you'll be digging at it with a screwdriver to try to get the handle lock to move.
The Pro2 seems to be more affected by having the in-tank outlet below the water level -- I think the priming button only has so much head that it can handle, if the outlet is also under water it has to push twice as much water to get the siphon going if it was interrupted.
The Pro has no priming button but does have the integrated taps and I have only cleaned it once so far, so I'm not sure if it is subject to any of these issues. When I cleaned it, I cleared the output line so it started right up.
So, yes, it will depend on the model, but that is why I have had to stop and think about the reasons behind the issues that each filter seems to have.
And clearing the tubes of junk by letting water out seems to be a good practice.
I can't really share much, since my only experience with canisters is with XP's, but once you have them primed, you never have to prime them again, unless you disconnect the hoses themselves from the unit for some reason.
With those models, it doesn't really matter if you fill them up or not. As soon as you close the quick disconnect, water flows into the canister through the inlet, air goes out the outlet. I fill mine up, because I don't want the scare the fish too much with the sudden bubble bath from the spray bar (which is located on the bottom!)
Yes, with a bottom spray bar, you would want to reduce the air volume by filling the canister first!
I can see that for many of the newer filters, this post will be irrelevant. But for the guys out there who are snapping up those old filters at garage sales or auctions, or buying used tanks with used filters, or are looking at the less expensive filters without the priming aides, maybe this can help. At least maybe I can save you a busted knuckle!