Sump size for 800 gal FOWLR

[scoupland]

I'm in the planning stage of 800 gallon (120"x48"x36") FOWLR. I want to be able to do 25% water changes (200 gallons) by draining the sump and then refilling it. How do I calculate the size of sump I need to do this? Here is my attempt.

As an arbitrary starting point I will use a sump with the dimensions of 72"x30"x26". If I multiply 72x30x26 that equals 56,160/231=243gal sump. Divide this in half (I am assuming the sump will be about half full when operating, and that gives me about 120 gallons of water in the sump. When the pumps are stopped and the display tank drains into the sump that would add an additional 118"x46""x??"=?? water in the sump. I multiplied by 118 and 46 to account for the glass thickness. How many inches will drain out of a typical tank--2, 3, 4?

If the tank drains 3", that would add 118x46x3/231=70 gallons from the display into the sump. 120+70=190 gallons which is just shy of 200 gallons. I guess I also have to consider that I won't be able to drain the whole sump due to baffles separating a section of sump. I would be using an external skimmer so there would be no water displacement with it.

Thoughts/help welcome.

 

[muttley000]

How much will drain out depends totally on how you set it up when you drill and plumb it.

 

[scoupland]

Thanks for your input.

 

[Marc]

I'm in the planning stage of 800 gallon (120"x48"x36") FOWLR. I want to be able to do 25% water changes (200 gallons) by draining the sump and then refilling it. How do I calculate the size of sump I need to do this? Here is my attempt.

As an arbitrary starting point I will use a sump with the dimensions of 72"x30"x26". If I multiply 72x30x26 that equals 56,160/231=243gal sump. Divide this in half (I am assuming the sump will be about half full when operating, and that gives me about 120 gallons of water in the sump. When the pumps are stopped and the display tank drains into the sump that would add an additional 118"x46""x??"=?? water in the sump. I multiplied by 118 and 46 to account for the glass thickness. How many inches will drain out of a typical tank--2, 3, 4?

If the tank drains 3", that would add 118x46x3/231=70 gallons from the display into the sump. 120+70=190 gallons which is just shy of 200 gallons. I guess I also have to consider that I won't be able to drain the whole sump due to baffles separating a section of sump. I would be using an external skimmer so there would be no water displacement with it.

Thoughts/help welcome.

Do you have any pics or drawings of your plans for the setup? It's kind of hard to understand what you want to accomplish without drawings or photos. Once I see that I could give you definate answers. As for water changes, in a FOWLR tank, changing the water from the sump doesn't keep the sand clean or liverock decor. I have a large system too and I shut everything off before doing a water change and use stored saltwater for the replacement. That simple. Don't try to get to technical such as gallonage changed out as this won't help decrease nitrate levels. You need a sulfur denitrator for that and a large skimmer to help decrease DOC's. A wet dry for that size system is not a bad option either as liverock by itself is not always enough to handle the biological demand of a FOWLR system. Trust me I know!

Marc