What would cause water level in overflow to fluctuate?

[Hypnotoad]

Hi everyone,

I've had a 29 standard with an external overflow box in a Herbie configuration up and running for a few weeks now. Rocks and inhabitants were transferred from an old 25 cube.

Yesterday I was home all day as my kid's daycare and my work were cancelled when most of town shut down for heavy snowfall.

Sitting next to the tank I noticed something kinda odd.

First I heard the telltale sound of trickling water than means my overflow level is below the standpipe, so I closed my gate valve a smidge and all was well.

Then the trickle again... closed the gate valve a tiny bit again.

This went on over the next few hours until I closed the gate valve by about a quarter turn.

This initially made sense to me, as I figured flow must be decreasing as the return pump/line must be getting a bit gunked up after running for the first 3 weeks or so.

Then a few hours later, the standpipe was gurgling the way they do when they're drawing in too much water, so I basically repeated the process in reverse, quieting down the overflow by opening the gate valve up over the next few hours until I was right back where I started (I know because I marked it)

Had I gone to work like any other Monday, I would have come home and everything would be normal and I'd have had no idea about the changing water flow.

So my question is... why does this happen? Something about ambient temperature, humidity, C02/02... barometric pressure maybe?

Anyone experience something similar and know the cause?

 

[Jeto2004]

Do you have power heads or wave makers in the tank with changing patterns? I gave up to tune a perfectly silent overflow with power heads changing constantly the amount of water that is pushed in the overflow.....

 

[Mical]

Do you have power heads or wave makers in the tank with changing patterns? I gave up to tune a perfectly silent overflow with power heads changing constantly the amount of water that is pushed in the overflow.....

I discovered similar when I switched to MP40s. My ATO hi sensor would trigger "on" maybe twice a day. Then comparing times of day to other things in tank, it was in fact when the MP40s kick into nutrient mode.

 

[Hypnotoad]

I do have 2 mp10s on either side of the tank running anti synch reef crest, so this would make some sense as a potential cause.

 

[Jeto2004]

I do have 2 mp10s on either side of the tank running anti synch reef crest, so this would make some sense as a potential cause.

Yup!

 

[Greg P]

so this would make some sense as a potential cause.

I'll bet this is what you are seeing.
It's happens in my tank very regularly and often over a 24hr period. I use a varied custom programming with my 4 MP10s in a 75g.
I set my tank level when the pumps are in a calmer state and ignore it when I get a little water down the emergency plumbing.
All I ever care about is the level never trips the float switch I installed in the back box, nor gets low enough to start sucking a lot of air.
It's been very stable for 6 months and when I hear it I take a look out of curiosity and that's about it.

 

[ca1ore]

Or it could be variations in the flow of your main pump.

 

[Greg P]

Or it could be variations in the flow of your main pump.

That and/or an ATO fluctuation is also very plausible

 

[Crabs McJones]

Do you have power heads or wave makers in the tank with changing patterns? I gave up to tune a perfectly silent overflow with power heads changing constantly the amount of water that is pushed in the overflow.....

Nailed it!