i am going to get a 150g tank... it comes with 3/4 inch drain holes on each overflow.,....the guy at the lfs said he would have them drill the holes bigger before it was shipped out. how big should i get these holes drilled????? he said 2 1/2 inches....would i have to have a huge pump to return all of that water????? i know i need alot of flow , but would 1 1/2 inches be ok???
Tank drilling question
- Thread starter ronj
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Krish
RF STAFF
You can have a 3 inch holes drilled if you wanted...It will only drain the water into your sump at the same rate (gph) as what is pumped into the tank. So in otherwards IMO, you can't have too big of an overflow, but you can have too big of a pump 
how will it only drain the same amount as what is being pumped into it....the water will drop below the overflow level and then the pump will have to cach up to it to get the water level back up to the overflows.......right???so there will be a delay in the overflow if it is dumping tons of water into the sump and the pump cant keep up??? i have never used a sump or overflow in a tank, so i am trying to get this
Krish
RF STAFF
Not really. When you shut off a pump that is in a sump, the remaining water which sits in the overflow will drain into the sump and nothing more because the water level will drop below the overflow, thus preventing anymore water from draining. When you switch back on the pump (say it is 1200 gph pump) it will be pumping the water back into the tank from the sump at a rate of 1200gph and nothing more which means the water will fall back to the sump at the same rate as it is being put into the tank/overrflow. Same goes for pre-filters like CPR overflows. The CS100 is rated up to 800gph. You pump 800 gph into a tank with the CPR CS100 connected to it, and it will return the same amount. You pump 500gph into that same overflow and it will only return the same 500gph. Or another way to look at it is imagine using a hose to put water in your tank. When the water gets to the top, it will overflow onto the floor at the same rate as the water is being added to the tank by the hose. If you turn the hose on MAX you will flood your house a lot quicker than if you had the hose set to just trickle. Same surface area for the water to spill over, but just at a different rate. I hope that made sense
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james734
Well-known member
He might be saying 2-1/2" hole for a 1-1/2 bulkhead. Not a 2-1/2" pipe.
http://www.marinedepot.com/aquarium_plumbing_parts_fittings_bulkheads_strainers.asp
http://www.marinedepot.com/aquarium_plumbing_parts_fittings_bulkheads_strainers.asp
Krish
RF STAFF
LOL...If you really think about the whole thing, it is understandable how it can get all confusing to understand the physics behind it all, because what you are saying/thinking how it should work, I would think the same way. It's only because I've had experience with a few different types of overflows, and sumps that has helped me to understand how it all works.
he was talking about the bulkhead holes...he said, the bigger, the better...i still am wondering, if the overflows are dumping tons of water down, what if you have a pump that is too small??? will it back up the water in the overflows if the pump cant handle as much water as is being dum ped in??
Krish
RF STAFF
Nope!
The overflow can and will only dump what is being put into it. It can't dump what isn't there. So if the pump is only feeding the overflow 1200gph, that is all the overflow can dump at the same rate being in a "closed loop". check this link it's can help
http://dslinux.dyndns.org/~denise/aquarium/DIYPlumbing/futureindex.html
http://dslinux.dyndns.org/~denise/aquarium/DIYPlumbing/futureindex.html
james734
Well-known member
The overflow will only drop what the pump can push over into the overflow box. if the pump can only push 1200gph over into the overflow box that's all the overflow is going to drain.
Krish
RF STAFF
LOL...K think of this again (I'm not all that great with examples
) You have a tank, that has a bulkhead in the side at the top with a 2 inch pipe running down on the outside like a drain. You fill the tank up to that bulkhead, and stop there. Now if you got a bottle of water and slowly poured it in the tank, the water level would rise slowly (at the rate you are pouring it in) and then at that same rate, make it's way into the plumbing and drain down. Then, you do the same thing as before, but this time, you get a hose and turn it on full blast! The water will rise at a quicker rate in the tank and drain down at that same speed. It can only drain at the rate at which the water is being added to the tank and nothing more. If you turn off the hose, then the water stops draining.When you have a prefilter plumbed into a sump from the tank, the plumbing is always full of water once it is primed. It is not like it just sits there with an empty overflow and plumbing. The water just stops flowing at the overflows cut off point which is below it's input level (when the pump is shut off), but water remains in the plumbing, sump and tank because it is all tied into once "closed system" DId that work any better???
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james734
Well-known member
Makes perfect sense to me. Good example..
i called all-glass mfg...they said that with the holes that come drilled already, the overflows handle about 600gph each.....he told me to return both overflows to the sump and run them with my mag12 back up. but the mag12 doesn't pump 1200gph at 4ft..it is more like 900gph...i am thinking about a mag 18...it will pump somewhere right at 1200gph at 4ft.....he said i can get the bulkheads drilled bigger if i want, but then i would have to modify the teeth on the overflows because they only allow for about 600gph each
the mag12 won't push enough gph..the overflows canhandle1200gph together....if i use the mag12, i will only get about 900gph....i have a 72g right now and the mag12 pushes just enough flow...i don't think it will be near enough for a 150g
yes it will be low then 1200 gph but i put my mag 12 and the return and the drain are full open (the valve you can see at the picture) i don't need to adjust the flow if you take the mag18 and the flow will be more then the drain you will need to close the drain little bit so it's not sure that you going to push 1800 gph , maybe try like krish to add the quite one 6000 it's more flow then the mag 12 but it will be less heat.
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