125 gallon reef sump setup

[reefmandan]

Are you drilling your tank? I think it's very important to include an emergency drain, which can also function as a trickle when using a herbie style overflow. If this tank is reef ready, it should be drilled twice in each overflow. I would suggest using one hole as a drain, one as a trickle/emergency, and on the other overflow use one as a trickle/emergency and the other as your return. This will also cut down on the number of ball valves, as you would only need one for the siphon drain. Trickle drains do not require ball valves. I would also suggest a check valve for your return line, depending on what kind of back-siphon situation it could cause.

Using your return pump as a feed for reactors is great, but can add a little extra vibration, so keep that in mind. On a tank that size, I don't think the heat from extra small pumps will matter much, really the only downside is having to use an extra plug.

I'm not sure about your ATO, but your sensor/float valve will need to be in the return chamber of your sump, and I suggest placing the hose from the ATO pump into your drain section, so the pure RO water has a chance to effectively mix with saltwater before moving into your display tank.