HOB overflow box, what am I doing wrong?

Huh? All overflows? Forgive me, but out of the 100 or so HOB overflows I have come across, I have only seen about 5 total that wouldn't break syphon, all others I had to do the "Aqualifter" trick to them to make them work if there was a power outtage.

The ones I have seen most of the time look like the one in the picture.. they do not restart the syphon by themselves when power comes back on. Please explain to me what happens then the tube loses suction and the water drains out? Your left with an empty tube of air right? Then when power comes back on and fills the box on the inside of the tank, it doesn't magically start to go up the tube, you have to either use an aqualifter or an air tube and manually suck the air out to get the syphon started, correct?
pca-overflow-box.jpg


I understand more expensive overflow boxes do provide continuous syphon, but the "normal" cheap overflow box that 90% of the people seem to buy doesnt.
 
Usually there is a small half-wall in the back side between the drain with the sponge filter and the u-tube end, although (as pictured) cheaper options sometimes don't. The solution is to use a short piece of pipe in the bulkhead so the end is higher than the end of the u-tube, which has the same effect of maintaining a higher water level in the box, to not let air into the u-tube.
 
The only way it is going to loose siphon is if the drain side piping is too low or it does not have enough water in the overflow side of the box. Usually the u-tubes will be longer on one end than the other. It is important to have the longer end in the drain side or you risk loosing the siphon...

Another important not is keep these adjusted to have just enough overflow to get the surface scum off, this will minimize bubbles and when the pump turns off there will be enough water in the overflow side, if not you risk loosing siphon.

If you are getting bubbles accumulated in the siphon, it is not set right. Once you get it set correctly, you don't have to worry about checking. I usually check it when I do a water change which is not every month. If there is any air in it, I usually just shake it up and down until it is clear or will remove it and reset the siphon with a airline sucking out the air...
 
sploke said:
Usually there is a small half-wall in the back side between the drain with the sponge filter and the u-tube end, although (as pictured) cheaper options sometimes don't. The solution is to use a short piece of pipe in the bulkhead so the end is higher than the end of the u-tube, which has the same effect of maintaining a higher water level in the box, to not let air into the u-tube.
Click to expand...

exactly how mine is...so, when the power goes out, both sides of the u-tube are submerged underwater and water stays in the u-tube. In fact, every overflow box i looked at had this feature.
 
Our u-tube has never lost siphon as a result of the countless power outages we have here in SC. The u-tube is equal lengths on both ends and doesn't require an Aqualifter pump or anything similar.

The siphon is not lost during a power outage because the drain in the box on the outside of the tank is higher than the end of the u-tube (or has a baffle to regulate the water height where the end of the u-tube is). When the power goes out, the water level will fall to the level of the drain (or that baffle), but no further water is siphoned because the water level in the box on the inside of the tank equilibrates with the water level in the box on the outside of the tank. Both ends of the u-tube remain underwater. In a properly designed / properly functioning u-tube overflow box, no air is introduced during a power outage to break the siphon.

If I were you, I would check the u-tube for air bubble accumulation every day since it's new and because I'm paraniod like that. If after a week you see no or virtually no accumulation, I'd feel more comfortable letting it go with just infrequent checks. However, algae will grow in the u-tube, so it will at some point be difficult to just take a quick peek to see if there's any bubbles.

FWIW, in the 3 years ours has been running, it's never broke siphon and I've cleaned the u-tube only 3 times (a LFS here has one that's been running 10 years+ years that's never broke siphon). Once the coralline algae starts to build up in the u-tube, it can greatly restrict the flow and I've noticed that it begins to trap more air bubbles once this occurs. With our u-tube overflow box, I can shake the u-tube pretty good without raising the ends out of the water to help break up any pocket of bubbles into smaller bubbles that will then get carried out of the u-tube by the flow. I only have to do this once the algae in the u-tube reaches a certain level, and that's generally the first indication that it's getting close to cleaning time.
 
thanks for the reply fsn...one more question: When the water drains onto the drip plate, there is a fiber pad that goes across it. Not only does it restrict flow and cause some water to flow to the side and completely bypass the bio balls, but i fear it is also is going to be a nitrate factory when it becomes biological. I have prefilters on both of the overflow bulkheads, so would I be ok removing this pad?
 
I've never used a bio-ball style sump, but the one person's tank I was really familiar with that did removed that pad. He found himself rinsing and cleaning it rather frequently just to keep it clean enough so water would flow through it. It's there mostly to catch any particulates so they don't accumulate on the bio-balls. The pad is probably finer than the foam pre-filters on the overflow bulkheads. You'll likely find yourself frequently rinsing those pre-filter foam pieces to prevent any sort of "nitrate factory" conditions from forming. But, you are removing that detritus from your tank each time you clean them. It's just something else to keep in mind when you are doing your regular maintenance.
 
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