That sucks. I would drill a hole in the magnum where you want the siphon to break. It will need to be below the normal water level if you want to keep it off most of the time to save power. If you'd rather keep it on for the flow rate, then you can put the hole above the normal water level and the siphone will break instantly during a power loss ie no drainage at all when the pump is off. Either way IMO you had the right idea with the hole. If you simply switch the returns it will continue to drain until the bottom of the other tube which will still be in the 20 gallon range.
Bottom line, your sump is too small for the amount of tanks/water you're running into it. Ideally you would want something in the 125 gallon range. Now you don't see a novice on drainage, you likely don't need to go out and find a bigger sump so much as you need to setup an overflow tub for power outages. Set the overflow to pick up below the top of the sump and then simply have this drain into say a 45 gallon tub from walmart. No need for a pump its merely an emergency overflow, not something you want to see happen very often.
The fish loss is a separate issue if you catch a power outage when you're home it's one thing. You need some kind of contingency plan for when you're not home. My bet would be a bubbler for each tank run by a ups. Hopefully it should last long enou for you to get home.
Bottom line, your sump is too small for the amount of tanks/water you're running into it. Ideally you would want something in the 125 gallon range. Now you don't see a novice on drainage, you likely don't need to go out and find a bigger sump so much as you need to setup an overflow tub for power outages. Set the overflow to pick up below the top of the sump and then simply have this drain into say a 45 gallon tub from walmart. No need for a pump its merely an emergency overflow, not something you want to see happen very often.
The fish loss is a separate issue if you catch a power outage when you're home it's one thing. You need some kind of contingency plan for when you're not home. My bet would be a bubbler for each tank run by a ups. Hopefully it should last long enou for you to get home.
