Buying a new tank, built-in overflow question

[lazuruskfp]

Hey all,
Starting shopping for 55-90g tanks to replace my 29g reef tank...
This time around I want a sump to improve my reef and I have been looking at the merits of a built in overflow, but I have some questions and salesmen at most places I go are f'n clueless. So here goes feel free to answer 1 or all and thank you in advance:
1) The overflows I have seen have holes at the top of the chamber and bottom... so does this mean even if my pump dies a horrible death in the sump the overflows will still keep dumping water down? :scared:
2) Some overflows have 2 outlets, and "experts" at the store say one is for return and one is the drain.... so how does the return work doesn't it just return the water right back into the overflow chamber? (seems counter productive) :notsure:
3) What are the merits of a overflow as opposed to an overflow box (U-tube)?
I mainly just don't want to flood my apartment... so I need to know everything before I get into the next level of reef keeping.
Thanks again,
novice aquarist :happyfish

 

[rbaldino]

1) The overflows I have seen have holes at the top of the chamber and bottom... so does this mean even if my pump dies a horrible death in the sump the overflows will still keep dumping water down? :scared:
I had an acrylic tank with a corner overflow that just skimmed from the top, so I'm not certain about the ones with upper and lower slots. I imagine they would both drain your tank until it's almost empty if the pump goes out.
2) Some overflows have 2 outlets, and "experts" at the store say one is for return and one is the drain.... so how does the return work doesn't it just return the water right back into the overflow chamber? (seems counter productive) :notsure:
The outlet nozzle should return water back into the tank.
3) What are the merits of a overflow as opposed to an overflow box (U-tube)?
They do the same thing, but the big disadvantage to an overflow box is that it hangs on the back of the tank (kind of ugly and in the way) and it can be difficult to maintain the siphon.

 

[lesleybird]

No, you won't flood your apartment with an overflow. You have some type of sump below and there will be two levels of the water.....one level when the pump is running and another one when the pump is off. The water stops flowing through the holes in the overflow when the water level in the tank is below the level of the overflow holes. This means that when the pump in your sump stops water only continues to flow until the water in the tank is just below the overflow holes which maybe only a few gallons. The sump should maybe be half full when the pump is running and maybe nearly full within a couple inches of the top of your sump when the pump (or power) is off. The trick to not having the thing flood your apartment is to finish filling the tank when the pump is off looking to see where the water level stops in the sump. Then when you turn the pump on see where the water level is and add your top off water to your sump to about this middle ground level. It sounds difficult but is really easy. If people had flooding problems they would not be so popular. I had the same worries before I got my 90 gallon but have not had any miss-haps with my overflow yet. The only advice I would give is to get a sump that is large as you have more play in the water level before your sump or wet/dry filter would overflow. Make sure that the sump that you get will actually fit through the doors of the stand you get.
Some of the reasons that having an overflow is so popular is that you don't get that nasty scum on the water surface and you get excellent oxygen exchange at the water surface as the water surface is constantly changing. The water gets additional oxygen when it falls over the overflow and through a wet/dry. If your built in overflow is too loud with the water falling you can fill it with bioballs. I have one of the Oceanic tanks that is several years old with the older overflow verson and not only do I have bioballs in my overflow, I also throw micron filtration pads scrunched up on top of thus making a filter out of my overflow. I do my "fish" laundry when I clean the tank meaning that I take these reusable micron filtration sheets and throw them in the washer alone with a half a cup of fragrance free bleach (no soap). I then remove them and soak them in water with a couple of caps of chlorine/chloramine remover for fish tanks. Unfortunatly the newer Oceanic tanks have a different type of overflow which could still be modified to make a filter out of it. Most people have bioballs in their sump's wet/dry area but I have one of those Tidepool things with filter media in it and a bio wheel thing in it. The filter media rarely gets dirty because of the micron filter pads I stick on top of the bioballs in my overflow. I just kind of scruntch these up on top of the balls and the water flows over and through these large rag type filter sheets. No need to cut them to form. I really like having my skimmer in my sump as my Coralife skimmer does tend to overflow at times. One last thing.....do not get the 55 gallon tank as you will reget it and want the 90 gallon within a month or two and it really does not cost that much more or take up any more length. Buying the bigger one a year later is more costly than getting it to start with. The ninety is no more work than the 55.....I started with a 45 and quickly had to get a bigger tank in less than a year. Most of the fun saltwater fish need at least a ninety gallon tank and you can only stock about a third of the amount of fish per gallon compared to freshwater fish.
As to the other person's comments on the overflows that water holes on the top and the bottom they will not drain your tank. The water flows through a chamber and cannot drain your tank. Google All Glass overflows or Oceanic's new overflow and you can find a diagram showing you how it is just as safe as the older overflows. It cannot drain the whole tank! No one would buy such a tank...their engineers are not stupid. Good luck, Lesley

 

[trainfever]

Actually, if you look at the overflows with the holes at the top and bottom, you will notice that the overflow has two walls. The outer wall has holes at the top and bottom but the inner wall has openings only at the top. The theory is that with holes at the top and bottom, the water will be pulled from several layers of your tank, thus filtering the debris better. When the water passes through the outer wall, it has to go over the inner wall. The inner wall prevents flooding because the water level in your tank wont get any lower that the top slits in the inner wall.
As far as the two holes. The salesman is correct, one is for your drain and the other is for your return. You would have to install a bulkhead into each of those holes. The larger one is for your drain. A pipe is installed into each bulkhead. The pipes are as high as the inside of your tank. There is a kit sold separately that has all the parts, it is called an overflow kit.
The merits of a built in overflow is that you dont have to worry about flooding once it is set up properly. If you lose power, your tank only drains to the top of the inner wall of your overflow. When the power comes back on, the water fills the top and drains as usual. With an overflow box, if you lose power, the water drrains up until the end of the U-tube, thus breaking the syphon. When the power comes back on, the water will be pumped up into the tank but since the syphon was broken, the water will not drain out and flood over the top of the tank.