Question about filter hook up

[Mouflon44]

I am building a plywood tank that will have a 3" lip around the top. I am also planning on using a few canister filters.
How do the filter hoses go in and out of the tank? Over the lip?

Would it be better if I drilled holes in the back for the inlet and outlet. I have heard of bulkheads (but don't know exactly what they are), is this what I would need? I know nothing of these canister filters... do I sit them on the stand beside the tank or underneath it in the stand, or does it matter?
I haven't started on the tank itself yet but I will need to know how this works before I do. I look at pictures of all these tanks with pvc looking pipes sticking through the back of the tanks. What equipment uses these? I assumed the filters. This post probably needs to be in the newbie forum, but I wasn't sure. :)

[OrionGirl]

Canisters usually run with tubes that pass over the lip of the tank, but can be hard-plumbed through the side as well. Bulkhead fittings create a water-tight seal between the side of the tank and the tubing--the bulkhead goes through the side, with a piece on each side that screw together and allow fittings for PVC or other tubing.

Canisters can be placed in either location, but you'll need to look at the rating (GPH/ft) to decide what works for you. Canisters will pump less gallons per hour if the head (height from the canister to the output) is higher, meaning less turnover for the tank.

HTH

[Mouflon44]

Thanks! I think I'll go with bulkheads and sit them on the stand beside the tank to provide maximum gph.
Do both the inlet and outlet holes need to be near the top of the water level?
Where is a good place on-line to buy the bulkheads and other fittings I need?
Thanks again!

[JSchmidt]

I was under the impression that canisters, by virtue of being a closed system, were not limited much by head considerations. Since unfiltered water drops from the tank (thru the inlet) into the filter as filtered water is expelled from the canister, I thought the effect of head was minimal.

I was under the impression that the main restricting factors on canister output were friction (as water passes thru the hoses) and the extent to which the filter media (in the canister) restricts flow. In other words, the main purpose of the canister filter is to pull the water thru the media. The fact that the system is closed puts less strain on the pump than, say, that of an open wet-dry, sump-based system. Am I mistaken?

Jim

[OrionGirl]

I'm not sure? I know that the canister I use flows more quickly if it's closer to the level of the tank than if it's on the floor. I agree, being a closed system reduces the influence of the head, so it maybe just be that the inflow line is seldom completely full, so bubbles slow it down.

For locating the intake/ouput lines--they neither 'need' to be located near the water line--it but it helps reduce flooding if something leaks. Also, the lines will need to be cleaned regularly, and if they are located too low, you'll have to drain the tank to that level to remove them. Always PLAN to have a flood, and then take very measure you can to minimize the amount of water that can come out. One way to do this is to install a valve right outside the bulkhead--you can also use this to help control the flow rate. You can always use PVC inside the tank to direct water returns to the depths of the tank.

Big Al's has a lot of parts--I'm not sure where else might. I have a very good LFS for most of that, so haven't bought very much online. And, of course, Home Depot/Lowe's are the place to get your PVC lines and elbows.

[Mouflon44]

Thank you. I will finish my stand this week, so next week begins the tank building!!!