Internal Toothless Overflow

[Poseidon20000]

All,

I'm in the design and planning stage of upgrading my 180 to a 220. I've been reading a lot about having linear flow and all the benefits it provides to the system. I've spent a great deal of time researching this site and other threads for GOOD examples of internal overflows without teeth to provide good linear flow.

I plan on purchasing an overflow box made by modular marine on ebay as they are willing to modify their units to my specs. I will run the beananimal on this box. See the attached picture. Their units all have teeth and they are willing to make one that is toothless. But, I want to get the communities opinion about the internal toothless box before I commit.

For those that have implemented this successfully are you using a modified box that has a horizontal split running across the box or are you just using a box that would have the same dimensions as a box with teeth and just having the water overflow into it? I have read others talk about a toothless box that has a lid to keep critters out? I'm having a hard time visualizing what this looks like because I imagined an open box with a lid but then that would be a closed box that water cannot flow into...

I dont plan on running super high flow through the DT, ill use power heads for that. I estimate less than 1500 GPH. RC calc says i need minimum 23" of linear overflow size. I plan on doing a 60'' internal overflow. As it is the 60" has teeth which would cut my linear overflow size down to 30''. I would like to go 60'' toothless but need more guidance on how this should properly work. Please post pictures if you have implemented this on your tank or if you have had experience with this I welcome your thoughts!

[Gorgok]

On mine the box just ends flat, water goes over it. No slot, no lid, no mesh or anything behind it...

With a cover you generally size it smaller than the box, so it sits inside the box with about 1/4" of clearance on the wet edges. The problem i have with that idea is then you have a dry shelf a fish can land on, which is then cooked by the lights. I'd rather have a fish in the sump than fried, unless its big enough to eat =P.

At 64" (estimate) of weir and 1500 gph of flow you would have a rise over the weir of 1/4" of water. That is basically what i have on my 75 with a shorter weir and a little less flow. Only thing to go over the weir so far are snails, but they go where they please anyway.

With an internal weir/external box like the one pictured you can put something to keep fish out of the siphon pipe and if they do go over the weir they end up just swimming in the external box until you retrieve it. No harm done other than maybe a little confused. Mine is also an internal weir/external box, though self made out of glass.

[Poseidon20000]

From the original picture that I have attached, the height of the internal overflow box measures 5.75" and is 1.5" wide with the teeth. Since the flow over the weir will be about 0.25" without teeth, do you think its best to make the internal box a bit shorter?

[Gorgok]

Thin water is less likely to attract fish i'd imagine, and will be most effective at removing the surface contaminant of the tank (and should be quieter, sticking to the sides of the box). I'd keep the weir as long as you can fit easily, keeping in mind any bracing and the physical size/shape of the box you are trying to fit in. Remember the sides add to the front length for total length too, so even if you are a few inches short on full with 2" of thickness you may end up longer than the tank is...

[Poseidon20000]

Originally Posted by Gorgok

Thin water is less likely to attract fish i'd imagine, and will be most effective at removing the surface contaminant of the tank (and should be quieter, sticking to the sides of the box). I'd keep the weir as long as you can fit easily, keeping in mind any bracing and the physical size/shape of the box you are trying to fit in. Remember the sides add to the front length for total length too, so even if you are a few inches short on full with 2" of thickness you may end up longer than the tank is...

Sorry, I meant to say shallower. The box measures 5.75" in height with teeth. Without teeth if the water moving over the weir is going to be roughly 0.25" in height I could technically make the box more shallow because the original was taller due to the height of the water being higher with the teeth. I know there needs to be a certain depth to keep it all quiet after the water sticks to the sides and flows down.

The internal overflow box will have two 2" bulkheads into the back of the tank glass leading to an external overflow box. There ill use 3, 1.5" drains for a beananimal.

I'd like to keep the internal footprint as small as possible. I think 1.5" wide and being over 60" long is great but if I can make the box more shallow that would reduce its footprint in the tank. But I don't want to making the box more shallow if it will cause excess noise.

[Gorgok]

Making it more shallow works as long as you can get the bulkheads far enough down the glass to be safe (diameter away from edges) and still fit in the box, and still hide the waterline.

This basically dictates the inside bottom of the box has to be 1.5x hole diameter + .5x bulkhead diameter down at minimum, and the top of the box should be at the same level as the trim minimum. With 2" abs bulkheads that is 1.5*72mm + .5*98mm = 157mm or about 6-3/16" down from the actual glass edge to the bottom of the box. With trim covering maybe 3/4" to 1" of the glass edge the box can be just a bit smaller than theirs is as stock.

[Poseidon20000]

Thank you! That was a big help!

[Kaidman]

If you're making this box 60" long you may consider adding 1 or more additional pass through bulkheads for more stability. My box from modular marine will arrive tomorrow. I had them add a third pass through bulkhead so the external box has more support. My box is 36".

[Poseidon20000]

How long was your internal overflow with your external being 36"? Did you also go toothless?

[Kaidman]

Both boxes are 36" in length. I chose to go with teeth since that is what he normally makes, so I'm expecting it to be quiet (I hope). I also had him add lids for the internal and external boxes to keep critters out. In my previous tank I had some fish get in the overflow that I could not get out which is quite frustrating. So I do not want that happening again.

If I were to get a toothless box from him I'd have him put the weir along the front, in the place of the teeth position if that makes sense. So the water wouldn't be going over the top of the box, it'd flow in from the front still, just no teeth in the way. Possibly have two rows of weirs to ensure I don't end up with a flood in case the bottom weir got clogged with algae etc. Since I want a lid for sure...

After I added lids to my previous tank overflows I never ended up with a cooked fish and the lid is much much larger than what we'll have on the modular marine boxes. A fish will just flop off the box without issue since it's less than 3" wide...

[FishN00b83]

Originally Posted by Kaidman

Both boxes are 36" in length. I chose to go with teeth since that is what he normally makes, so I'm expecting it to be quiet (I hope). I also had him add lids for the internal and external boxes to keep critters out. In my previous tank I had some fish get in the overflow that I could not get out which is quite frustrating. So I do not want that happening again.

If I were to get a toothless box from him I'd have him put the weir along the front, in the place of the teeth position if that makes sense. So the water wouldn't be going over the top of the box, it'd flow in from the front still, just no teeth in the way. Possibly have two rows of weirs to ensure I don't end up with a flood in case the bottom weir got clogged with algae etc. Since I want a lid for sure...

Instead of having the 1/4" slot in the front of the overflow (potentially 2), why not just notch down the lip in the front and have it completely open. You can still put the lid on the top and you would never have to worry about it clogging. A lot of tanks have a setup like this and I've never heard anyone complain about them. It would look something like this in the front:

|\___________/|

The water would just flow right over the lower lip and will never clog

[Poseidon20000]

That's a good idea as well fishn00b83! This would still allow me to add a cover. My sump's first chamber will catch all the water from the full siphon and then over flow to the second where the water will cascade down the filter socks. Should anything hitch a ride down the overflow they will most likely be caught in this first chamber. Since the first chamber will be mostly filled with water, whatever ends up here will most likely survive until I can extract it.

Kaidman, the main reason I'm planning the box without teeth is for the surface skimming. Your box measures 36" with teeth so that only gives you 18" of linear overflow. Those who have done glass C2C over flows that do not incorporate teeth and also claim their system to be quiet. I have seen on another site where modular marine made an internal for someone who had a thick eurobracing in the center and coundnt go C2C. So they made that reefer two externals due to the large gap. I believe that person had a 6' tank. Modular marine made two holes on each box on the medial ends which then drained from the far lateral ends of the external. I think that persons external was 24". The two holes on the medial ends of the internals seemed to be enough to support. I know that's kinda hard to visualize but it went something like this

_______--------+++------______

[Poseidon20000]

** correction. MM made them 2 INTERNALS connected to a single EXTERNAL

[thejuggernaut]

I built one almost exactly like what you are talking about. Mine is 42" long though. You can see photos over a page or two on the large acrylic thread.

http://www.reefcentral.com/forums/sh...56956&page=170

[Poseidon20000]

I have decided to go a full 70" of toothless internal overflow!

Inside box - 70" x 1.5" x 5.75" tall
Outside box - 24" x 4.75" x 6.5" tall

The external overflow will be 24" long and have a 2" bulk head at each end.

I think a 24" external overflow with 3 - 1.5" holes for a BA should be sufficient enough to handle the overflow from the 70" internal. I will also utilize an 1.5" single return that will 90 over the top of the tank and overflow and output about an inch into the water.

For those that have experience in this, do you agree with this set up? Is it sufficient? If not, what is your recommendation and why?

[Poseidon20000]

I have also read other posts but can seem to find a definitive answer on the shape of the edge of the top of the overflow.

Is a rounded edge better than a 90 deg square edge? Or does it matter?

Anyone???

[Gorgok]

When its that long it really shouldn't matter... The water will stick to the walls either way. Whatever you do will be temporary anyway, as growth and snails will make it a new shape in no time.

[thejuggernaut]

Make the external box taller. 6.5" isn't much to play with. You want atleast 2" above the top of your emergency drain. That leaves only 4" of water for your open channel and siphon. I settled on around 8" for my boxes. It gives more more head pressure for purging on startup, gives you more room to adjust your running water height. Mine is tuned in so well that on startup the water level never even touches the emergency drain. It literally only sees water when both the siphon and emergency both clog. I would put the bulkheads half way down the external box, so that you can adjust your running water level to be about about 4-5" deep and have the water level at the middle of the bulkheads. You'll also need to offset the box from the tank with a spacer so that it clears the rim, so you can have the external box sit level with the top of the tank. Also, get slip x thread bulkheads for your drains. That way you don't have to run PVC adapters. They take up too much height.

[Poseidon20000]

Thank you! This is great