Herbie / Durso Overflow Decision

SoCalVictor · Sep 27, 2019

I recently got a used 180 gallon acrylic that I'm looking to set up right away. It comes with two corner, triangle overflows, each with a 1.5" and 0.5" hole.

I was originally wanting to use a Herbie style overflow and based on what I read, it is recommended to have the larger hole be for the emergency standpipe and the smaller hole for the main siphon. This means I use a 0.5" hole for the main siphon which I'm afraid is too little flow. My target flowrate for a return pump is in the 2000 gph and I'll supplement with a pair of MP40s.

I'm not able to drill additional holes in the overflows so I'm not sure I have any other options except to use the 1.5" as the durso, unless someone tells me it's ok to use herbie style with the 1.5" be the main siphon.

Any thoughts on recommendations?

Quietman · Sep 27, 2019

Not sure a durso would handle 2000 gph return either. Think the max for 1.5" is 1500 gph. Likely you'll have to cut flow either way....but many have 5x or less tank volume per hour just fine.

SoCalVictor · Sep 28, 2019

Well, with the two overflows, I have a total of 2x1.5" holes. I'm open to cutting down my flow. Is there a way to accomplish the herbie?

Silent · Sep 28, 2019

You have 4 holes. You dont have to make both small ones siphons. You should use 1 small and 1 large siphon and use the other 2 for emergency drains. That way you can get the flow you want and still have 2 emergency drains.

SoCalVictor · Sep 28, 2019

Not a bad idea. With the large and small siphons in two separate overflows on opposite side of the tank, I'll get disparate downflows with the two overflows. Will that be an issue?

Quietman · Sep 28, 2019

Right....4 holes. Not

Silent said:
You have 4 holes. You dont have to make both small ones siphons. You should use 1 small and 1 large siphon and use the other 2 for emergency drains. That way you can get the flow you want and still have 2 emergency drains.

Right 4 holes...great point. Or you should be able to split the supply into the two .5" and use the two large as full siphon and backup.

Silent · Sep 28, 2019

Put a gate valve on each siphon and tune them separately. As long as both drains combined match the flow of the return pump you will be good. Doesnt matter the number of drains or size of drains as long as drain flow = return flow.

HOOPDEEZ · Sep 28, 2019

Seems like you would want them balanced. I would run two 1/2” full siphons, you should be able to get around 800gph each out of them, so with head loss on the return, it should be close. Put a valve on your return and keep on rockin. Or use a smaller pump(s) you don’t really need 2000gph return for that size tank. The only flow that you really need to match is your skimmer rating.

Goodair · Sep 28, 2019

You only need 360-900 GPH (2-5x) in terms of your turnover. The rest of your flow should come from your power heads. Your stock, rockscape and power head positions will play a more important role with flow for corals amd should dictate how much extra flow the tank needs.
That 360-900 is AFTER headloss btw.

SoCalVictor · Sep 28, 2019

@HOOPDEEZ It feels like I would want them balanced but I can't think of a solid reason why. Thoughts?

@Goodair I was considering sch 80 bulkheads so for the 1/2" bulkheads, that flow will be even less right?

ca1ore · Sep 28, 2019

Can you not ‘over drill’ the holes for the 1/2” bulkheads? Acrylic drills pretty easily and you could do it from underneath. Drains in independent overflows can be tricky to synchronize, so setting it up as two separate herbie is best. There’s really no need to use sch80 bulkheads. If your 1/2” holes will accept a 1/2” sch80 bulkheads then they’ll also accept a 3/4” sch 40. Latter will be better.

SoCalVictor · Sep 28, 2019

RIght now, the tank is drilled for 1/2 Sch40. Might actually be tough to go bigger for a few reasons

1. I might not enough clearance with the tank wall and also the 2x4" supports on the edges of the stand
2. Hard to over drill the holes since w/o something to grip the pilot, the hole saw will skip/walk. Unless I clamp some kind of jig... I thought about screwing a pvc plug to a bulkhead, then install the bulkhead, then drill the hole around the bulkhead using the pvc plug as the grip for my pilot.

JoshH · Sep 28, 2019

SoCalVictor said:
RIght now, the tank is drilled for 1/2 Sch40. Might actually be tough to go bigger for a few reasons

1. I might not enough clearance with the tank wall and also the 2x4" supports on the edges of the stand
2. Hard to over drill the holes since w/o something to grip the pilot, the hole saw will skip/walk. Unless I clamp some kind of jig... I thought about screwing a pvc plug to a bulkhead, then install the bulkhead, then drill the hole around the bulkhead using the pvc plug as the grip for my pilot.

Using a tapered bit would widen the current hole as long as theres room to do so and you don't have to offset the hole to make it larger. If the holes are drilled for Schedule 40 bulkheads you won't be able to use Schedule 80 bulkheads of the same size and I don't think you want 1/4" returns lol Not really required as schedule 40 is plenty for our plumbing applications

HOOPDEEZ · Sep 28, 2019

I have a single overflow, so I’m no expert, but I would think that you would get the same amount of water going over both weirs. So I would think that even if you had a 1.5” full siphon, you would have to tune it down to match the 1/2” full siphon or the 1/2” overflow would back up and the emergency on the 1/2” main side would be doing extra duty. It may not matter, but it’s less of an emergency if it’s already having to deal with the extra water flow, and the emergency on the other side with the 1.5” full siphon only has the 1/2” durso for backup. It’s less room for error if the main clogs, and I would personally not roll the dice. I think you would be surprised how much the 1/2” full siphon will pull. Theoretically it can pull 1180gph each, but I said 800 to be safe. But like I said I don’t think you need that much flow through your sump, use your power heads for flow in the tank. I personally would get two smaller pumps as your return, so you have a back up if one fails and aim for around 1,000-1,200gph total

SoCalVictor · Sep 28, 2019

In my previous tank, I used a single durso (no emergency) and I did not have issues. I'm wondering if the best route is to not use the 1/2" holes and just use the two 1.5" holes with two dursos and toss the idea of a herbie style. Any concerns/drawbacks with this?

Goodair · Sep 28, 2019

1/2" is pushing the lower limit for 420 gph gravity flow. That is just water draining naturally with no pressure.

Schedule 40 and 80, for aquarium purposes is the same. Only difference is cosmetic.

Idealy, You want to be using 1" for the main drain. this lets you able to adjust the gate valve to balance the herbie drainage method.

Goodair · Sep 28, 2019

If it was me, and drilling wasn't possible, along with not wanting to add the return to run along the back of the tank, I'd do this:

Use the 1.5" holes, 1 for main drain, other for emergency.
And run 2 smaller return pumps instead of 1 big one through the 1/2". Where the 2 pumps push the same amount of water as the single pump. This is good incade 1 pump fails, the other will keep the water going if your not there.

Only cocern with this is the water in the overflow section with the emergency flow will have low turbulance. Someone might have a better idea.
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Or what would be better is the have 2 herbies, and run the returns in the back of the tank if your ok with the extra piping.

SoCalVictor · Sep 28, 2019

The tank actually already has two 1/2" additional holes on the back of the tank. I'm intending on using them for the returns. So actually I have 6 total holes

1.5" hole in each of the 2 overflows
0.5" hole in each of the 2 overflows
0.5" x 2 holes on the back of the tank

Goodair · Sep 28, 2019

do 2 main drains with the 1.5, 2 emergency with the .5, and use the 2 back ones for ur return.

I forgot the depths, but make sure the main drain is a certain diatance below the water line. You can easily search this up. The emergency lines need to be around the same height, nuy chances are 1 will be alot dryer than the other which is ok.