success possible with HOB overflow/return?

[Gobynoob42]

So, I might be stuck with an undrillable 37gal tank (can't find recipt). So I'm looking into other options.
I'd like to still run a sump (since I built one), and haven't heard to many good things about canister filters.
I'd like to have fish and soft corals.
Is there any way to get reasonably good results with a HOB overflow/return? This is one product I'm looking into:

https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/112832156878

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[cracker]

Over the back overflows have been around for a long time. There is an inherent risk of loosing the siphon though . That's where the new internal overflows come in handy. I have used HOB's for many years & never had a problem. If having the tank drilled/internal overflow installed is not on Your list I'd say go for it. Just make sure You understand how they work . The HOB probably leave more room in the tank.

 

[DaveK]

The overflow box you are looking at looks like a CPR overflow, see this link (offsite) - https://www.cpraquaticinc.com/cs-overflows/

In my opinion, this design has so many design defects that it will easily cause floods. I recommend avoiding this design at all costs. Here are the major issues -

It is impossible to clean the siphon area. Note the baffles around the siphon area. These make it impossible to get any kind of cleaning too up inside it for cleaning. This can allow it to clog and cause a flood.

The wide U siphon easily traps air bubbles, causing the siphon to break. If this occurs, you have a flood.

To attempt to avoid the previous problem, they recommend using a small pump such as an aqua lifter to constantly remove air bubbles via the small connection at the top of the siphon. This small connection tends to clog. If that happens, you are back to the previous problem.

The small connection at the top of the siphon easily breaks off. If that happens the siphon will break and you have a flood.

I speak here from bitter experience, since I at one time had a CS202 on my system and had all of the above problems with it, plus some additional ones. When I replaced it, I smashed it to bits to avoid inflicting it upon some other unsuspecting hobbyist.

If you need to use an external overflow box, by far the best one out there is Livereef. See them here (offsite) - http://www.lifereef.com/siphon.html I know, they cost about 3x the price, but the siphon tubes are removable, cleanable and replaceable.

Another possible alternative is an Eshops overflow box. They are not as good as the Lifereef, but the design is at least acceptable. You can see them here (offsite) - https://www.drsfostersmith.com/product/prod_display.cfm?pcatid=18358

 

[Gobynoob42]

Thanks for the sound advice!

I see the potential problems with the HOB stuff. 1. Power outage, 2. Loss of siphon in overflow

I'm looking into a battery backup for the power outage, https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/173143680325

How can I prevent the loss of siphon in the overflow? Will the air lifter automatically kick in once the siphon breaks? Or does it run continuously?

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[DaveK]

Because of their design, the overflow boxes I mentioned do not loose their siphon during power outages. Loss of siphon due to air bubbles is unusual because the round tubes tend to pull any bubbles right through.

However, you still need to worry about power outages. The main problem here is preventing the return plumbing from back siphoning, that is flowing in reverse, and draining the tank. The best solution here is to drill a small hole in the return pipe just above the water line in the tank. Then if flow stops, air will enter the hold and break and the siphon. Alternatively you can also use a check valve. If you do that, you do need to clean and test it regularly. Otherwise the check valve will not seal properly if the flow stops. This is because SW tanks get a lot of growth everywhere in the system. It only takes a few tube worms growing on the check valve to make it fail.

Battery backups are of some, but limited value in SW systems. They can keep circulation pumps going for awhile, but if you try to use them to keep a main pump going, you will typically tend to drain them very quickly. A return pump uses a lot more power than a circulation pump. Some people that have a lot of power outages have installed backup generators. This does work well, but it is expensive and has it's own set of problems.