I tried to build one a few years ago, but I was so nervous about it busting a leak under pressure I converted it into a sump. It is a challenging project, and you will most likely not save any money since commercial filter companies can make a custom plastic case that can take the pressure for much less than a home tinkerer. Even if you only use PVC the cost of the fittings, piping, and a decent pump will put you at least within the price range of a reasonable store unit. That said I know a lot of DIY-Savvy types have made them with success and a quick google for DIY canister filter raised a lot of the same guides I was looking through when I attempted the project. I am not sure the forum legality of posting outside links so you might have to search for yourself. Good luck!
Step 1: Go to LFS or online shopping site.
Step 2: Select canister filter
Step 3: Open wallet
Step 4: Purchase canister filter
Step 5: Go home and set up your new canister filter and smile knowing that you
didn't pay a lot more money to rig up something that will end up in a
spare parts bin.
I have read somewhere around a hundred DIY ideas for canisters. Ten percent swear they work fine but the other 90 percent just swear to never do it again. It really is hard to come up with ideas that have not been tried. For fun it might be fine but for really saving money-- you can do better picking up cans!
There are a lot of different DIY projects depending on your interest. A fun entry-level one that is pretty easy to get into would be making a small led moonlight, they look pretty cool and even if you bork the project it is usually under $10 wasted, if that.
Some other low cost DIY projects? How about sponge prefilters, DIY nets, Tank dividers that don't collapse, Covers to keep fish in but let air out, DIY lights or if you are into wood work, stands and canopies are always a good item.
Unfortunately the DIY canister is appealing but often not practical. Guys often have a fair amount of time and money invested before they find what they want is not very much fun to maintain after they get it built. Water has a nasty way of finding a way to get out and onto the floor!
what materials cover a tank but let air out ? the moon lights are an idea.
How can I add more circulation in the tank? I've seen the wave makers and stuff for salt water but what can you use with fresh water tanks and with shrimp?
That's another reason I wanted to add a filter for more circulation. I have some BBA that won't go away and was thinking that might help it.
I use light diffuser panels (eggcrate?) from the drop in ceiling section for tank covers. If I want to use them for dividers for fry, I cover them with wedding veil (tule) from a fabric store. Wedding veil costs about a dollar for 36" X72" and comes in real handy for making super large nets and all kinds of weird things when you have it.
I find simple cheap powerheads for circulation when I don't need more filter. I do really like Koreli for good quality powerheads as they are quieter.