3/4” Return Lines causing changes in return pump flow?

[Cameron Smolinske]

On my 170 tank I have a 3/4” return line that splits and feeds 2 separate lock line returns into the tank. Ever since I’ve set this tank up I’ve noticed that I am constantly having to adjust my gate valve on my drain line because of fluctuating levels in the overflow box, which in turns causes a change in the level in my sump which causes issues with my ATO. Are the 3/4” lines the cause or could there be something wrong with my drain line? Return pump is a Sicce SDC 9.0 (older model) TIA for any help

 

[KrisReef]

When the drain flow is unstable, the level in the sump will reflect this. The most dramatic results from starting and stoppping of full siphon in one or more drain pipes. Getting all of these things balanced out can sometimes be a challenge, and in other set ups they just flow evenly on start up.

The return pump, if it is old, may contribute, but in general I would suspect that the drain is cycling between full siphon and siphon failing? Do your drains make noise, and does the noise change or cycle?

 

[Cameron Smolinske]

When the drain flow is unstable, the level in the sump will reflect this. The most dramatic results from starting and stoppping of full siphon in one or more drain pipes. Getting all of these things balanced out can sometimes be a challenge, and in other set ups they just flow evenly on start up.

The return pump, if it is old, may contribute, but in general I would suspect that the drain is cycling between full siphon and siphon failing? Do your drains make noise, and does the noise change or cycle?

Drain doesn't seem to go from full syphon to failing syphon. Pump is only about 6 months old but is the older style SDC with the elongated controller. Being that it was probably New Old Stock I am starting to wonder if that's the problem. However there is no noticeable cycle to it happening. I usually notice it if I am sitting near the tank and I hear the ATO running constantly.

Kind of at a loss at what to do that doesn't involve replacing the return pump and upgrading the return plumbing to mostly 1".

 

[mfinn]

If you can post pictures of the return lines, where they split and go to the tank.
Post pictures of the drains in the overflow box and under the tank. And gate valve.