I set up my new tank yesterday, I posted a big description here: http://www.bettafish.com/showthread....=2#post1399073
I am using the no-name HOB filter that came with the tank, but I replaced the media with Aquaclear 20 sponge and biobag that I had previously bought for my Azoo Mignon 60 filter.
I didn't want to use carbon. So, I jammed two of the sponges in the chamber, and the biobag on top. This does not quite completely fill the chamber up to the lid, there is some space on top of the biobag. The filter flow is adjustable and I have it turned down as low as it can go. The top of the biobag is sitting out of the water slightly.
My question: is this ok? Should the chamber be filled to the very top? Seems to me it wouldn't matter, as the water is not going any higher anyway. Is it a problem that the top of the biobag is not submersed?
This is also just a general HOB question, too. I've noticed this with every one I've examined. It seems like a funny design to me. What is preventing the water from just flowing through the biobag on top and out? Will the water really be flowing down into the sponge and back up again? Seems to me like water would fill up the sponge and then just mostly stagnate in there, maybe very slowly cycling up as more water pours in, but once that chamber is full of water it seems to me that the "path of least resistance" would just be to flow straight to the outfall - bypassing the "layers of filtration" down in that chamber. Hmmmm.
Thanks for any insight into how HOBs work!