Frag tank addon to system

I need some suggestions. I've been wanting to add a frag tank to my existing tank setup for a while. My sandbed is littered with zoas



I'd like my display to look more like a display with a nice white sandbed and have a frag tank for all my easy to cut zoa frags on tiles.

My current setup is a 90 gallon display with a 40breeder sump. I've already purchased a 40 breeder for my frag tank, a glass-holes.com overflow kit, and my lights will be on the way this week. My problem comes from the fact that when I built my sump I was thinking water quantity and so right now when I shut the pump off on my system there's only about 2" of room at the top of the sump. I'm afraid that if I plumb this new tank into the existing sump it will be too much and overflow the floor. Being a poor college student, I'm trying to do this as cheap as possible.

Here's my idea and I need advice as to whether this will work or not. I did a little crappy paint diagram to show what I'm thinking: Red is for return lines, blue for overflow lines. The green line would be a constant siphon between my existing sump and a rubbermaid container.


I figure as the water is pumped into the frag tank from the rubbermaid it will drive the siphon to refill it and therefore maintain the water level in both the rubbermaid and my existing sump. Then when I turn the pumps off the siphon can equalize the water level between both and give me some much needed extra space water quantity. Will this work? Has anyone tried it? Or does anyone have a better idea? I'm space restricted on the left side of my existing tank so I need to put the frag tank on the right, and I can't think of any other way to link the frag tank in. I really don't want to maintain 2 separate systems.

What do you mean check valves? The only check valve I'm familiar with is like the ones you'd put on an airline.

Your drawing looks like it would work OK but I would want to take steps to assure the constant siphon doesn't break. If flow through the siphon isn't strong enough to purge any small air bubbles that might enter the siphon they could slow the flow and eventually break the siphon. You could plumb in a small aqualifter pump and have it come on for a few minutes each day to make sure the line is free from air. 

So if I understand your diagram, the rubbermaid container is for additional water capacity so your sump doesn't overflow in the event of a power failure, or just when the main pump is off, correct? that is a good thought. They do make check valves (one way valves) for pvc so in theory you could omit the rubbermaid sump expansion. HOWEVER, I am always very cautious about relying on check valves, because I have seen them fail and it's not pretty when they do. In my experience, it's not a question of "if" but "when" they will fail.
In regards to the siphon, the most reliable way to feed the expansion tank would be to connect the two near the bottom (below the water line), so that way the water just flows between the two without worrying about breaking a siphon. That's obviously more work than setting up a siphon because you'd have to drain the sump and drill it, but ultimately it's a little safer bet in terms of water flow.
Anyway, just offering suggestions to think about.

Edited by Deluxe247 - March 26 2011 at 11:22am

Could you take some pics of the space you have to work with and how much space is behind the sump as well? It would help us give some practical suggestions. I am having trouble visualizing how everything is currently set up, what else is in the room or rooms and developing my thoughts. Without knowing exactly how your existing tank is set up and what the available space for the frag tank looks like it is difficult to give you a workable suggestion.