Canister filter, sponge filter questions

Can a canister stay on during a water change? Depends on how the intake is built, and how deep it draws from.

There aren't many for 20 gallon tanks. Toms Rapids, I think, is the only one that comes to mind. Canisters are going to have lower projected GPH ratings, but they tend to be more true ratings, through more crap.

Don't know about CO2 injection.

Infusoria and such? Other than being moved around differently, I doubt it would be impacted.

No different impact on fertilizer than your HOB, all things being equal. In other words, if you're running carbon (or any other media) in your HOB, and you run it in your canister, and the media impacts the efficacy of your fertilization regimen, the effects will be the same.

So far, I open up and clean my CF400UV every 2 months, but I've only had it for about 3. I had some issues with it at first, but tech support was very helpful. That said, when I started rinsing sponges, they were *filthy*, so it seems it's doing quite the good job.

How messy it is depends on your particular set up. I know I'm getting the hang of it with mine, and while messier than a HOB to clean, it's not horribly so, and it'll get better as I get more used to the routine with it, I'm sure.

If you can break a filter, you can break a filter.

I use an AC 20 sponge block, cut to allow the intake to fit into it to prevent stuff from swimming in. I'm sure if I crack it open right now, I'll still have 20 or 30 shrimp in there, though. They still manage to find their way in, somehow.

A prefilter (use an AC 20 sponge block, it's orders of magnitude better than most premade sponge prefilters, but if you can get a stainless steel mesh one, that might be a good alternative) will help prevent the filter from being clogged by moss. AC has the most versatile and effective HOBs on the market, it seems. The Fluval C series (basically upgraded AC, by the same parent company) is very nice and in some ways better. That said, it's not anywhere near as versatile.

Sponge filters are absolutely horrible for any kind of CO2 injection, because, by necessity, there are a ton of air bubbles to facilitate the off gassing of your CO2. I have an Ista Bio-Sponge filter, and it's small, black, and with a nice weight at the bottom.

Sponge filter with a powerhead is more of a prefilter scenario, from what I understand.

I don't know if fry or infusoria or whatever would get into the filter. Frankly, I think the shrimplets *try* to get in there, and work their way in through the pores or something. Drives me nuts. If the pores are too fine, you'll find yourself with suction issues, as your prefilter melds to the intake and prevents flow. It's pretty crappy when that happens.

I release the suction (the step I've forgotten to do and would have prevented at least some of the mess) and remove the top, leaving the top connected to the tubes. How heavy depends on the canister. I'd imagine one for a 20 gallon tank isn't going to hold much water volume, so it should be relatively light, under 10 pounds or so. I'd imagine the vinyl tubing will eventually deteriorate, but being much thicker than airline tubing, it should last much longer before it's noticeable. I'll probably think of replacing mine in a year or two. My LFS actually has black vinyl tubing for not much per foot, so I *may* replace the tubing sooner, but I doubt it. I did not notice a temperature increase. That said, I was already working on slowly increasing my tank temperature (in preparation for getting rams) when I set it up, so any increase could have been hidden in that. I think the smell issue comes from water being in there, and sitting for a while. Since the water in the canister is almost always flowing, I doubt you'd find a noticeable odor that's any different from your tank in general.