Herbie drain - Fluctuating overflow level

[Potatohead]

This is my second tank with a Herbie, they work well but I am finding I get about 3 - 4 cm of fluctuation in height in my overflow box. My old tank wasn't super stable but probably better than this one so far. I can adjust and it will stabilize, go back in twelve hours and it has hardly moved, but then another twelve hours later it has moved a couple centimetres or something. My plumbing is as simple as it gets, I just have a straight drain to a 90 and then soft tubing in a soft bend to the filter sock. I literally have my gate valve sitting vertically on the filter sock mount. I am using an ATO that allows about 1.5 cm return chamber water level difference from high to low.

This tank has been running about three weeks. Will this possibly become more stable in time? Should I run a trickle down the emergency? Should I run a ball valve on the return and throttle the pump (Tunze 1073.02) back just a touch? Is this kind of normal since filter socks don't always allow flow through at the same rate and/or because of atmospheric pressure?

Thanks

[lyall12]

I had the same problem, and found time and small adjustments were the answer. As your pump and pipes build up with stuff the flow rates will change.

I'd do super small adjustments on your drain at a time and wait and see how it reacts.

I go through the same process when I clean my pump, everything needs some tweaking.

And as long as you aren't flooding the emergency, or dropping so low you lose your siphon you should be fine.

As far as a trickle on emergency I've seen arguments back and forth. Some say it's a good way to get extra surface skimming. Against say that even a trickle of water could lead to build up and blockage of your emergency line. I avoid it as my emergency drain exits above water in the sump so I can hear when something is wrong.

[Potatohead]

I'm hoping it will settle in time. When I make the adjustments I am turning the valve the smallest amount I can feel, like maybe a 2° turn. I'm hoping it's stuff building up in the pipes and it will settle down.

I designed my system so that even if I lost all draining from the display, the return chamber is sized and the ATO is on a time limit so that it will never be able to pump enough water to flood the display tank. That will likely kill the return pump but that's not a huge deal... So I am not too concerned about running a trickle if I have to (I have tried it) but if the trickle becomes a little larger trickle it starts to make noise.

At the end of the day I'm not all that concerned with it because if the level falls a bit, it's still quiet which is the main thing for me. My only real concern is that let's say the ATO fills the return chamber to the max level, then the level in the overflow falls over the next couple hours, this raises the level in the return chamber even more and it sometimes triggers the high level alarm on the ATO, which is annoying. Or, the opposite happens and the swings on salinity are greater than they should be (albeit still small).

[iamfrontosa]

Need to make sure that the main drain is clean.

[Potatohead]

Need to make sure that the main drain is clean.

Brand new

[input80]

I had the same problem & found it was my DC return pump. Changed it out & everything has been fine since.

[WarDog]

I had the same problem & found it was my DC return pump. Changed it out & everything has been fine since.

+1. DC pumps are notorious for causing fluctuations in flow.