Restarting Return Pump

[newsalt]

I have a 120g reef and a 55g sump. On my sump, I put a line to indicate the operating level of the sump. My ATO is set up so as not to fill the sump up past this line.

Everytime I feed the fish, I turn off my return pump. It stays off for about 20 min. When the return pump is off, the water level in the sump rises higher than the operating level line.

After the 20 mins., the return pump comes back on and the water in the sump begins to lower. Problem is that it lowers to about an inch below the operating line level and always turns the ATO on filling the sump with RO/DI.

Why is this happening? If the operating level in the sump before I turn off the pump is right at the line, why then when the pump comes back on does the water go below the line? I would think that the volume of water that drains into the sump when the pump goes off would be the same volume of water going back to the display tank once the pump comes back on. Could it be something with the drain line?

Any ideas?

[timespinner]

I can think of several possibilities:

1) You are losing water somewhere (a leak)

2) The system needs some time to come to back equilibrium after the return pump is restarted.

I'd guess that what you are seeing is #2. A larger drain line could help the system come back to equilibrium more quickly, but it could also mean more noise depending on your overflow.

[drstupid]

i vote for timespinner's second possibility.

do you have a controller? or are you manually turning off your pump to feed?

if you have a controller, and you are using the feed cycle to turn off your return, and you are using a pump for your ATO not a gravity feed, then you could add a rule to keep the ATO pump off for some period of time (5 minutes or so) after ending the feed cycle.

[newsalt]

Thanks for the replies.

I don't think it's a leak only because I don't see any water on the floor or anything. I'm going with #2 as well. The drain line is 1-1/4" and the return is 1".

I'm using an AquaController and using the Feed Cycle to turn off the return pump. That's a good idea about putting in code to keep the ATO off. Thanks.

[drstupid]

i saw a post on the neptune vendor forum here on rc about doing the same thing to delay a skimmer from restarting after the feed cycle shut off the main pump until the sump level dropped enough to get back below his skimmer output. same problem, you could copy and paste the code that was posted. but i can't find the post. if you were to post the question there, i'm sure someone would give it to you before you went to bed tonight.