Physics of a sump. Why does it do what it does?

[Dankrencisz]

Again, please forgive my ignorance on this but the physics behind the return chamber of my newly installed sump is making me scratch my head.

So I have a 75g DT with a 20g high diy sump 300gph overflows, mag7 return pump (choked back).

The water level in the return section is almost always fluctuating. Example: yesterday I added my usual gallon and a half of pure water from evaporation. This is about what I evaporate ever other day. As I added the RO/DI water to the DT, the volume in the return of the sump dramatically increased.

Why? How does the volume of water in the display tank change the volume of water in the sump return? Should I have added the top-off water to the sump?

I'm asking because I travel occasionally for work and the DT has to be wife or teenage daughter friendly.

Just curious. Thanks.

 

[duperdave]

I hope I can explain this right.but due to the way the water flows through your system the only place you're going to notice the missing water from evaporation is in the return section of your sump.I always added the water to the return section.put a full mark on the glass so that they know how much water to add .

 

[SS_Sean]

The return pump and drain being set at what they are in your system, will keep the DT at a certain level. The pump is pumping X amount of water into the DT, and the drain is draining Y amount to the sump. What you did when you set your system up was balanced X and Y, so that they are essentially equal in the DT. You lose the water due to evap in the sump. However, if you poured your top-off water into the system in the DT the water will be high for a little bit in the DT, but will drain off, and end up re-stabilizing again. It's just my opinion but I like to put the top-off water in the sump, that way I don't have to listen to the gurggling of the herbie drain, and the RODI water gets dispursed through the nozzles into the DT for less problem with disruptive specific gravity levels of the salt.

 

[bundybear1981]

As Dave said, the overflows in the dt should keep the water level in your dt constant. The sump on the other hand will drop volume from evaporation. I add my topoff water to the tanks overflow / weir (I use an ato) so it blends before hitting the dt.

For making it easy for others to assist I would mark the sump either with pen or tape and fill it to that level.
For long term I would encourage an ato - makes life easier and keeps the tank more stable.

 

[Dankrencisz]

Thanks. Definitely an ATO. Still working on getting a protein skimmer. ATO is the next gadget after that.

 

[SS_Sean]

They're cool. I'm still playing with getting my ATO set. As mentioned, mark your sump for the amount of water that will not overflow your sump in case of power loss. If the power cuts you will get a certain amount of drain-back and the sump has to handle that amount of water, or you're going to have a big mess.

 

[DaveWJunior]

Go to your kitchen sink and place a tall drinking glass into a cereal bowl.
Fill up the glass all the way to the top but only fill the bowl half way.
Now pour water into the glass.
The glass (display tank) which is already full, dumps the excess into the cereal bowl (sump) which is only half full.
Science lesson over.

 

[Dankrencisz]

Science lesson over.

That is a great example. Thanks.