Why I'm ditching my herbie style overflow
 

Herbie style overflows definitely have their place in this hobby. When they are set up right, they give you all sorts of control over the noise level in your tank, and prevent your overflow from becoming a sludge filled accidental refugium. However, I've discovered that they're not appropriate in every circumstance. When I was researching how to set up my tank, I never found a thread that explained why they wouldn't work for me specifically (and thus my current predicament), so here's hoping I can help avoid this PITA for someone else.

When Herbie overflows work great:
If you have one overflow on your tank, or if you have two overflows that are completely separate. It also helps if your auto-top off system adds water relatively slowly, and if your return chamber is large relative to your sump.

When Herbie overflows are not the right choice for a system:
If you have two overflows that are plumbed together before they exit in to your sump so that you only have one pipe depositing water in to your sump, and when your return chamber isn't very large relative to your sump. My plumbing is set up this way, for a few reasons that aren't relevant to discuss here, but one of them being that I only need to use one filter sock. Originally, I believed that placing the gate valves that controlled the herbie's above the point where the pipes met would give me individual control over the height of the water in each overflow chamber. I was mistaken. Even though the pipes connect downstream of the gate valves, the whole system still functions like one unit. I can set the height in the overflow chambers for maybe a day, then over the course of a few days, one overflow chamber will progressively fill up, while the level in the other will fall. Once that happens, adjusting the height of the water in the overflows is extremely difficult, as adjusting one overflow will have secondary effects on the height in the other. I gave up months ago trying to have both overflows set at the level I wanted and accepted that only one would be below the main tank's water level. They are also prone to freak out if you put your hands in the tank for maintenance. I've had my herbies (whose dials hadn't been touched in months) fill up spontaneously and start pouring down my emergency drain simply because I started turkey bastering my rocks.

I then added a single gate valve downstream of where the overflow pipes met to see if I could 'Herbie the herbies'. This works, but you still have no individual control over the water level in each chamber.

There also seems to be a relationship between the height of the water in the overflow chambers, and the height of the water in the return chamber of your sump - that isn't as obvious as it sounds, I promise. For example, if you have your herbie set and running perfectly, then you add a few inches of water to your sump, the water level in your sump will eventually fall back to where it was initially set. This has the side effect of filling up your overflow chambers by the same amount of water that was added to the sump. This isn't a huge problem unless, like I did yesterday, you add a more powerful pump to your ATO system (the R/O reservoir is in the basement and the pump I had wasn't cutting it). When the Tunze osmolator brain kicks on, it runs for a set number of seconds before it can shut itself off. In a sump with a relatively small return chamber, and a powerful ATO pump, this means that the osmolator actually overfills the return chamber slightly (water completely submerses the sensor) before the osmolator turns itself off. It did this all day, overfilling the return chamber, which then filled up the overflows in the display tank by a small amount, then evaporation triggered the sensor again, which led to overfilling of the return chamber again. Process repeat until water was pouring down my emergency drain standpipe.

Anyway, I'm going to get the parts together for a DIY Durso this week. In my application, herbies are more trouble than they are worth, though I'm sure for someone with a much simpler plumbing set up, they would work beautifully.

Interesting write up, thanks for sharing as this is EXACTLY what happens in my set up! Except my drains are completely separate and not plumbed together. I'm manually topping up my tank ATM, filled this morning, overflow also filled.

Hmm will follow along to see how your new system works for you.

I think the return chamber/overflow water height relationship thing is a function of the herbie system in general, regardless of how you have it plumbed. I'm not a physicist at all, but in a 'normal' overflow, the overflow pipes always have more capacity to drain than the return pump can pump, do any added water to the system falls to the lowest point in the system (the return chamber). This adding more water to a normal system just increases the return chamber water level.

In a herbie, the draining capacity of the overflow pipes is throttled, so the height of the water in the overflow and return chamber become highly related variables. Basically, I think that the height of the water in the overflows (and thus the return chamber) becomes a function of the restricted rate of flow, and the total amount of water moving through the system. If you add more water, rather than "falling" to the lowest level like it would with a normal overflow, it gets "held" above the point where the flow is restricted. Essentially it means that you need an ATO that adds exactly the amount of water you need and no more, otherwise you risk slowly overfilling your tank.

maybe i missed it but do you have standpipes in your overflows?? this would keep your height set ,your gatevalve fine tunes the rest to a syphon ,trying to tune a herbie wthout standpipes and just the overflow boxes is a losing battle imo.

also if both drains run into the same pipe at the end, your safety feature of the herbie is useless as one drain shold never hold water un less its needed, and if by chance it was needed you wouldnt want your emergency to be blocked b y whatever is blocking your primary:)

I use a herbie system on my 6' tank.

Here are my particulars...

Tank has dual corner over flow boxes, both double drilled. Left side, I use one hole for my return pipe. Right side has my emergency drain.

Both sides submersed drains are plumbed exactly the same, same fittings, same length of pipes, everything. Under water they both have a 6" threaded pipe that connects to a threaded 1" tee. The tee has one 1" strainer horizontally, one 1" strainer vertically pointing up, the bottom is threaded into that 6" pipe.

Underneath the tank, all pipe is measured so that my true gate valve meets exactly in the middle. I did this so that the force of gravity from each side would be the same.

Height was a problem with my setup. My gate valve is actually lower than the top of my sump which sits on the floor of the adjacent closet. This means the draining water must travel up about 5" of height before draining into my sump. Both the emergency drain and the gate valve line are on seperate drain lines into the sump. Because of the height, I have to ensure my emergency drain always has a trickle of water moving through it, otherwise the water sitting in the dip would go stale and bad.

Because I am already slightly taxing my emergency drain, I use a fairly weak return pump. I have fully closed the gate valve to test the capacity of the emergency drain, which it handled.

I should add I use an ATO, but my sump system is 90 gallons total, when the ATO shuts off, the sensor is NOT fully submersed under water.

I did have standpipes, but all they do is set the minimum water level, and if you hit that, it makes an awful sucking noise. The second time that happened (as one overflow filled up and the other emptied), I took them out.

And the emergency drain is a totally separate drain. I have two overflows, with two holes in them each. The south end has an overflow and the return, the north end has an overflow and the emergency standpipe, which goes straight down to the third chamber in the sump

the way Im reading it, the problem isnt with the plumbing inside the overflow box, it is the fact that the two drains are plumbed into one on the bottom side of things.....that is a major herbie no-no....two drains into one is creating back pressure which is why its causing noise and stability issues.........and just to correct what Denny said:wink:....there is no syphon with a herbie....it is purely gravity that feeds it(like a bathtub or toilet)....

Damn the fella that helped me out put 2 drains into one fml...... I am goin to be in need with changing things up I think, I am new to the hobby and didn't know any better

Maybe I missed something in the reading