Trying to estimate how much water would be drained from a 150 gallon marine land tank when the pump shuts down. Does anyone have one that can either calculate the volume their sump fills when the pump is off? I’m upgrading from a 90 gallon to a 150 gallon and trying to see if I need a bigger sump or if I can use my current one. Thanks.

There is no exact calculation I can think of just because too many variables. Most important is where will the water level be the lowest in the DT before the back siphon breaks. More trial by error. First get a rough idea. Then simulate a power failure. Keep close eye, if you getting close to overflow kick the pumps back on and adjust from there Edit, forgot to ask what sump you have now?

Generic acrylic 30x14x16. My current back flow on the 90 gallon is 6.5 gallons and I have room to spare, probably 10gallon total volume empty when the pump is running. I’m thinking I will need to upsize, but if I do I want to have it on hand. I didn’t plan for an upgrade right now but a LFS has the 150 with a custom rock wall and stand for $400. They just broke it down and wanted to move it today for space. They were more interested in the livestock than the tank.

That sumps not a bad size. Bigger the better, but I have a Bashee signature 36 which dimensions are not much bigger on my 180. Got a deal on the tank, see if they could deal a new sump too. Can’t hurt. If not the tank sounds like a good deal, use the saved money for the sump. Not sure what the rock wall is though.

Back wall of the tank has egg crate siliconed to it, reef safe foam sprayed on and chunks of live rock stuck in. My 90 has the same.

Fill your tank, let the sump fill up from the overflow on its own till it’s at the max you want it. This is your max water level. Meaning if your pump fails the water won’t rise any higher. Plug your pumps in and you’re good to go. Should work...right?

For the most part, yes. When you fill the DT and keep going until the overflow drains into the sump it will give an idea. Once the pump kicks on the return pump chamber may empty out due to the water into the empty return pipe filling up. From there add water into the sump until the pump is not sucking air. About an inch or 2 above that should be good. Then do the test.

Easier test...fill tank until water goes into sump. Then full sump to about 1 inch below the top. Turn on your pumps...if you still have enough water in the return pump chamber then your sump is big enough. If this is not enough water then your sump is going to overflow during power failures and you need a bigger one. Doing it this way is safer than putting in all the water you need and hoping the sump will hold it when you test by turning off the power. Simply put all the water your sump will hold must be enough or have to get another one.

Those would all work, but the sump is in the stand of the 90 gallon which is running. I can’t take the sump offline and remove it due to the front brace and the fact the sump either needs to be removed from the top of the stand or the back. I would need to drain and empty the tank, move it and then switch the sump over just to test. That is why I asked if anyone had one of these tanks to get a ballpark figure on gallons of overflow during an outage so I could estimate if I needed a bigger sump.

See what you mean. There should be someone that comes along that may be able to figure out the volume. I would guess it should be ok. But rough guess. Your sump around 30 gallons. Mine is 37 on my 180. I have 2 returns and 1 siphon drain with 2 overflows. . If the 150 has only one it should be ok providing your sump has lots of room running the 90. Again just theorizing. Always stay on the saf side to avoid overflows i alway say

If the 90 drains 6.5 gallons at pump shut down (assuming it's a 48x18 tank, surface area is 864) so 6.5 gallons divided by 864= 0.0075 gallons per 1" surface area. Now multiply 0.0075 by surface area of your new 150 tank (in sq inches) to get volume of water that will drain at pump shut off. Realize this only works using the same pump with same flow rate, at same head height- if any of those factors change, then so does the amount of water going into the sump. HTH

You may find the following R2R article to be helpful (especially steps 1-16 at the end of the initial post): SUMPS - The Rundown. Additionally, the closer that you can get a siphon break to the surface than the less water will need to drain back into the sump before the siphon will break and stop the flow. _

I have a 135 gal with two 25 gallon frag tanks. The volume that settles on the sump is a function of the total surface area and the hold-up height. In my case volume varies from 10-15 gallons. When my overflow strainer (keeps small fish in DT) gets “dirty”, the hold-up height in the DT can increase by 1/4 inch. If power is off for long enough, this results in an extra 5 gallons in my sump. To eliminate this, I have to keep the strainer/guard clean.

On my 90 I have the returns lower so I could raise one and get the siphon break higher and actually not have as much drain back. I’m going to need to either play with this or just buy a bigger sump. Thanks for all of your help.

If you are not able to raise one of the returns high even, you can also drill a small hole (e.g., 1/4") just below the water level in one of your returns to create a siphon break. Good luck!

Well you can estimate with math. Lets say your sump has a bottom that is 4sq feet. And we will use 2 tanks with this sump. One is a standard 240 gallon 16 sq foot base area and one is a 4x2x2 120 which has an 8 sq foot base. Each inch the 240 needs to drain before the siphon breaks would add 4 inches to the water level in the sump 16/4=4 While with the 120 it would only add 2 inches to the sump per inch drained 8/4=2 . Generally you also want to consider the overflow and pluming to be about 1 inch of tank drain. So lets say your sump is 16 inches and you keep the water level at 8 inches. In the example with the 240 the plumbing and over flow would raise the sump 4 inches and 1 inch from the main tank would raise it another 4 inches and it's full. This means if you need to drop the tank more than 1 inch to break the siphons that 240 would overflow your sump. If we look at the 120 the plumbing and overflow count for 1 inch of tank which raises you from 8 to 10 inches in the sump. Draining 3 inches out of the tank raises the sump by 6 more inches and it's full. This means if you need to drop the tank water by more than 3 inches the sump will overflow. You can see the difference the tank sq ft base makes as with the 240 you can only drop the tank 1 inch while in the 120 you are able to drop the tank 3 inches. In short there is no way I would trust a sump that can only allow 1 inch of tank level to drop so that 240 would need a sump with a much larger sq ft base. I hope this helps. Keep in mind the math is only as good as how well you can estimate the #s you put into the formulas.

Well you can estimate with math. Lets say your sump has a bottom that is 4sq feet. And we will use 2 tanks with this sump. One is a standard 240 gallon 16 sq foot base area and one is a 4x2x2 120 which has an 8 sq foot base. Each inch the 240 needs to drain before the siphon breaks would add 4 inches to the water level in the sump 16/4=4 While with the 120 it would only add 2 inches to the sump per inch drained 8/4=2 . Generally you also want to consider the overflow and pluming to be about 1 inch of tank drain. So lets say your sump is 16 inches and you keep the water level at 8 inches. In the example with the 240 the plumbing and over flow would raise the sump 4 inches and 1 inch from the main tank would raise it another 4 inches and it's full. This means if you need to drop the tank more than 1 inch to break the siphons that 240 would overflow your sump. If we look at the 120 the plumbing and overflow count for 1 inch of tank which raises you from 8 to 10 inches in the sump. Draining 3 inches out of the tank raises the sump by 6 more inches and it's full. This means if you need to drop the tank water by more than 3 inches the sump will overflow. You can see the different the tank sq ft base makes as with the 240 you can only drop the tank 1 inch while in the 120 you are able to drop the tank 3 inches. In short there is no way I would trust a sump that can only allow 1 inch of tank level to drop so that 240 would need a sump with a much larger sq ft base. I hope this helps. Keep in mind the math is only as good as how well you can estimate the #s you put into the formulas.