HOB Overflow Help: Water level in tank not consistent

[kesuk]

I finished plumbing an old tank I had with a HOB overflow from Marine depot a few weeks ago and everything seemed like it was running smoothly until a few days ago. I added a skimmer to my sump chamber and a few hours later noticed the water level in my tank had risen to the point it was overflowing slightly. Luckily I caught this before any major damage was done, turned off pumps, adjusted and opened the flow up more and everything seemed to be working again. The part that confused me is that the second drain in my overflow never kicked in (I have it set up as a Herbie with one low and one high standpipe).

The water level in my overflow appears to be staying level while the tank level is varying. Since that first near flood, I've noticed that adding water to the sump seems to cause the water level in the tank to slowly rise and I'm constantly having to adjust the outflow of the tank to find an equilibrium. I was expecting that as things changed in the tank the level in my HOB would adjust and eventually the emergency drain would kick in to prevent flooding, which doesn't appear to be happening. Can anyone help explain why this is happening and what I might adjust to fix this?

Equipment being used:

LoPro External Overflow Box (400 GPH)

Fiji Cube's unique design takes low-profile overflows to the next level! We were immediately impressed by the thoughtful design and unique features of Fiji Cube's overflow boxes. The wet side overflow box is among the slimmest on the market, but what really sets it apart is the ease of...

www.marinedepot.com

Hygger 800GPH DC pump set 60%
10-gallon sump

Images of the setup below ( usually the standpipes have the black foam pre-filters, removed to show heights )

 

[W1ngz]

Not familiar with that particular overflow, but like most reefers I'm pretty well versed in how a siphon works so here's my guess:

Your pump is outpacing your overflow, but just a little which is why it takes a few hours for there to be a problem.

The speed that the water passes through the U tube in your overflow, from the weir side to external box is dictated by the relative difference in level between the tank and the external overflow box water level.

If you shorten your emergency to make the external box level lower, the outflow from the tank will be faster and be able to keep the water moving out of the tank. Start with a pipe about a 1/2 in shorter, and move on to 1" then 2" and see where it's happiest without making too much noise.

Remember to adjust the valve on the primary to keep up with the increased flow through the U tube.

 

[kesuk]

Thanks! I'll give that a try and see if that stabilizes it.

 

[Mastiffsrule]

Hi,

quick question

have you tried opening up your drain valve more to get more flow. It looks like your siphon is not flowing enough and your emergency drain is being used too much. The siphon should be doing the majority and the emergency should be dry.

 

[Marc2952]

I finished plumbing an old tank I had with a HOB overflow from Marine depot a few weeks ago and everything seemed like it was running smoothly until a few days ago. I added a skimmer to my sump chamber and a few hours later noticed the water level in my tank had risen to the point it was overflowing slightly. Luckily I caught this before any major damage was done, turned off pumps, adjusted and opened the flow up more and everything seemed to be working again. The part that confused me is that the second drain in my overflow never kicked in (I have it set up as a Herbie with one low and one high standpipe).

The water level in my overflow appears to be staying level while the tank level is varying. Since that first near flood, I've noticed that adding water to the sump seems to cause the water level in the tank to slowly rise and I'm constantly having to adjust the outflow of the tank to find an equilibrium. I was expecting that as things changed in the tank the level in my HOB would adjust and eventually the emergency drain would kick in to prevent flooding, which doesn't appear to be happening. Can anyone help explain why this is happening and what I might adjust to fix this?

Equipment being used:

LoPro External Overflow Box (400 GPH)

Fiji Cube's unique design takes low-profile overflows to the next level! We were immediately impressed by the thoughtful design and unique features of Fiji Cube's overflow boxes. The wet side overflow box is among the slimmest on the market, but what really sets it apart is the ease of...

www.marinedepot.com

Hygger 800GPH DC pump set 60%
10-gallon sump

Images of the setup below ( usually the standpipes have the black foam pre-filters, removed to show heights )

I have the same overflow box on my 75 gallon and found out that with time the u tubes will start to get clogged up with algae since they are clear, with time the amount of water that is siphoned is reduced which in turn affects the return section of the sump. I suggest painting those u tubes black or getting a cover so light doesnt reach it.

 

[kesuk]

Thanks for the ideas, as an update I did end up cutting the standpipes so the main drain is much lower and haven't had the issue since. I was worried about algae building in the tubes eventually but I'm not sure I'd want to paint them black as then I couldn't see if a bubble was formed when starting the siphon. I haven't had much build-up yet but I'll keep an eye on it.