Tiny overflow on big tank - useful?

Kind of a waste of money IMO to have an overflow and sump if you arnt going to use the recommended size for the tank it is on.

It would be alot cheaper to add a surface skimmer from hagen or eheim and just connect it to a canister.

Well if I have a sump, the probes can be in there, the fert can also be inject in the sump using gravity fed system, and water level is always maintain. So not just for surface skimming.

I like the idea, keep me posted on this..

The size of the overflow you need is dictated by how much water you want going down to your sump and by your return pump. Use a really small return pump.

But like fshfanatic said, if all you want is surface skimming and can work out the dosing issue by dosing directly into your tank, I think it'll be a better way to go.

Don't forget that sumps allow you to have a constant water level in your display tank. You can also do this with an automated top-off in your display tank, but that's more hardware, more cost, and more ugly equipment to have to hide.

I've been thinking a bit more about this. Having this small sump can also be beneficial in facilitating automatic water change. You would have two water level sensors in the sump, one slightly higher than the other (0.5" higher than max pump off water level) . The lower one will trigger top-off solenoid. The higher one will be use as a level sensor for the main tank. To do this, turn off the sump pump, then pump water out of the tank for a fixed time period. Now fill the tank, when the tank is full, water will overflow to the sump, thus raising the sump's water level, and eventually trigger the higher sensor. When this sensor is triggered, turn off water change fill solenoid, and turn back on the sump return pump.

What do you guy think?

Yeah that should work, just that youll have to have your pump in the main tank. With a larger sump you can do it all from in the sump and also not worry about shutting of your return pump - thats what I am doing. But for a smaller sump I am sure what you propose would be fine. The only thing I am leery about is the HOT overflows breaking siphon... could spell disaster especially if your automating the water change...

Yes, that's true if the siphon breaks, it's game over. So probably need to have a small "wire sensor" at the tank edge and/or timer as a contingency plan. I guess the benefit is that for those who want to remove equipments from the tank, a small overflow seem to be a viable solution. I checked with lifereef already, and they can build an even smaller overflow for me, 2" width outer box. And a short 4" height inner box. So such a small box on a big tank hopefully wouldn't be such an eye sore. Hopefully I can hide it with driftwood poking out of the water at around that area and plant anubias or something around that area.

Why don't you just buy a set of lily pipes?

I haven't get a clear answer on if lily pipes will help clear surface scum. I may have to buy the cheaper version to test myself.

Apparently they do, they cause a suction like a mini bathtub spinner which "eats" the surface scum, You made have to have it half raised though.