How to calculate overflow rating for a freshwater sump?

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gstrommen

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Oct 19, 2009
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I have a 300 gallon acrylic tank with a pre-built overflow. I bought the tank from someone on craigslist and I have had it setup for quite sometime although I am not using the overflow and I have never used a sump before.

I am doing the research on wet/dry filters / refugiums / and sumps for freshwater tanks. One of the concerns I keep coming across is that your overflow should be rated for more gph than your return pump so you don't overflow the tank. How can you calculate what your pre-build overflow is rated for? I obviously don't have a manual.

I want to try to cycle the tank at least 10x an hour. Taking into considerations plumbing joints, head space, etc. I am looking at pumps capable of handling 4500gph or more and I can always throttle it down with a ball valve after the return pump. Question... how will I know if my overflow can handle that?

I do have some other questions but that is first on my list.
 
Sump capacity is practically meaningless in this instance. The RC calculator works well. Why do you feel the need to turn the tank over 10x per hour? Half of that flow through a good wet dry is more than adequate. If you need more water movement in the tank add powerheads or drill for a closed loop.
 
The volume the prefilter could handle depends on the size of bulkheads and the # of drain holes in the prefilter.

I do agree that 4500 GPH maybe way overkill for f/w tank. If memory serves, 1" bulkhead can handle ~600GPH. If prefilter has 2 of 1" bulkheads for draining, should not return more than 1200 GPH in order to avoid any surging action/overflow.

Check the bottom of prefilter to determine size of bulkhead. Another word, Is it 1" or 1-1/4' or 1-1/2" PVC pipe to fit into existing bulkheads?
 
I am still researching this myself so if I am incorrect just let me know but this is what my research has yielded so far.

Take into consideration overflow teeth opening (if your overflow has teeth). Although my drain line in 58g can handle 600gph the teeth only allow about 300 gph through. This calculator, overflow calculator, works a little backwards in this situation but play with it and you will find the right combination. Note the linear overflow size is open space where the water can flow.
 
I want to start by thanking everyone who has responded.

I should have also mentioned in my initial post my existing filtration setup. I currently have a pair of Eheim 2080 filters. Each one is capable of handling the 300 gallon tank by itself. I have a pair because I believe strongly in having at least twice the necessary filtration on your system and if one filter fails, I have a backup already in place.

The main purpose of this project (besides the fact that it sounds fun to me) will be to allow me to have a place where I can have plants. Plants in my tank do not last long as they are either eaten or constantly knocked around by the larger fish. The purpose of the plants is to help lower my nitrates which are always high. I also want a place to put the heaters and get them out of the main tank. Eventually, I also plan on adding a UV Sterilizer to the setup on the return from the sump.

There is only one overflow built in.

Here is another piece of information and I do not know if it matters. The stand does not seem to be appropriate for the tank. It has the hole predrilled for the overflow but there are large supports (dividers) in the stand every 2' and there is no room for a sump inside. As a result, I will have to put the sump off to the side of the tank. (I will cover it and make it aesthetic looking later.) As the sump is not directly below the overflow, the water will have to go through some bends and angled pvc to get to the sump. This will probably have an effect on how many GPH can actually go through the overflow.



In response to dbosman,
Thank you for that link, it may come in very handy when I try to figure out how large of a sump to go with.

In response to SubRosa,
I have read that you should cycle your water at least 10x an hour through your sump. That is where I came up with that number. It may be overkill as I already have the two filters. Water movement is not an issue at all as I have both returns from the filters, two powerheads, and two air bubblers.

In response to Cerianthus,
Thank you for that suggestion on checking the size of the bulkhead. For some reason, that did not occur to me. I will have to get back to you on the actual size. Obviously, this is a very important piece to the equation.

In response to myswtsins,
Yes, my overflow has the teeth opening.

Here is a thought and everyone can correct me if I am wrong. When I get the initial plumbing set. I can raise the water level in my main tank to just where it would flow into the overflow. If I add 5 gallons of water (or more as long as I know the exact quantity) from a large bucket, and pour it all into the large tank quickly, I can time how long it takes for the water to go through the overflow. With some math, I can calculate how many gallons of water can go through the overflow per hour. Does this sound like a good idea?

I guess my next step is to figure out exactly how many GPH can go through my overflow so I can determine how big the sump needs to be and how powerful of a return pump I will need.
 
Hi
Can't help with your calculations but have you ever thought of than automatic water changer rather than sump?? Since the tank is already running a bit late for a gravel purger but could probably be done. You could use the sump for a reservoir but wouldn't run the overflow of course.
Run one on a 75 over 5 years and never changed the water by hand also never vacuumed lol. Would cost a lot less than a sump setup gary
 
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