Choosing a sump size for a 125gal

[Railrider1920]

I'm going to be getting a 125 probably in the next month or so. Under it the space I'll have will be about 49" long, 16" wide and maybe 30 inches high. I'll have to leave enough room so I can get my skimmer in and out of it. I have a 30 gal tank as a sump under my 75 now, using about 20 to 25 gal in it. I have access to other tanks to make a sump out of and I have some glass to make one out of as well.

Is there a rule of thumb for sump size for different tanks? Or maybe something like a sump large enough to hold X pounds of liverock for every gal of tank? How do I choose a sump for a 125? Suggestions on size welcome as well, but please include why I should go that size.

Thanks,
Rob

 

[killingseed2000]

make sure you have enough room in the sump for the 125 to overflow into when the power is out. what are the messurements of the 125. if its 72x18x22" then about 11.2 gl will drain before stop. i just used a tank calculater to figrure 72x18x2", 2" .

 

[Railrider1920]

72x18x22 sounds right. Thanks for the reminder. I was thinking about that.

 

[AZDesertRat]

I use a 30 G for the sump on my 100 G (60"x18"x23")and its about perfect. I can't imagine 2" would drain back in a power outage, I get about 4.6 gallons if an inch drains back but its always 3.5 gallons or about 3/4" or the height of the fingers on the overflow box. 2" seems extreme unless you have your returns low in the tank. I keep my returns close to the surface and have never had a problem in almost 6 years now. I always keep right at 8 gallons of freeboard or spare room in the sump even when its filled to the max just to be safe. No drilled holes in the returns or check valves both of which require maintenance and are a flood waiting to happen.

 

[Murfman]

I used a 55 under my 125, for a sump. Now my sump IS a 125 ;-)

 

[fishnreef]

I use a 30 G for the sump on my 100 G (60"x18"x23")and its about perfect. I can't imagine 2" would drain back in a power outage,

A couple of thoughts..
If you have high flow for the return loop, the water level above the main tank return will be high. If that drains, then you get additional water into the sump.
Also, if you have algae build-up, due to not having time to cleanup, that will result in additional water volume into your sump.
Larger is better than smaller. It's amazing how many things will conspire to overflow your sump.

 

[Sikryd]

Use the biggest you can fit under there and use the calculators on RC to make sure the overflow volume is right (when the pumps are shut-off)

I have some pictures around here somewhere of mine.

 

[Railrider1920]

Yeah I was going to go as big as I can. I have a 55 that has broken glass. I'll probably take it apart and fix it up to get it under there. I'm not exactly sure how far down the back glass the two holes are, but 2" is about right. The tank and stand are at a LFS about 1 hr or so away from me so I can't just drop by to measure things. I forgot to measure hole placement when I was there. I'll do that when I'm there next.

Thank you all for the replies, reminders and things to think about for sump size.
Rob

 

[AlexStinson]

i used a 55g under my old tank 60x18 and it worked like a charm

 

[xrayrider]

A 55 will work, but it is very tall and hard to get into when under the stand. I decided to go instead with a 60 gallon long. It is tight front to back, but fits nicely. You have a little more volume than a 55, and it is much easier to get into. I had room left over in length, as the 125 is 6 feet long and the 60 is 4 feet long, so I still had room to add a 10 gallon tank for my auto top off reservour. I think it is the best shape and total size for a sump under a 125. I filled it half way, so there is plenty of reserve volume to prevent floods, and enough extra space, for a huge refugium area.