sump level question?

[newfishliny]

just did a test run on my 90 gal , when the pump is off the water level in the sump is 5 inches , aprox 8 gals of water . the sump is a 20 gal long tank .
How much more water should I add to the sump , need some evaporation room , don't want to fill it everyday.
pump is a mag 7 , pumps 750 gph.

 

[oceanjumper]

I would say as much as your sump can hold in case of power failure.
I didn't like to check the top-off either, but you do not want salinity/gravity to fluctuate too much either. As such, I added an automated top-off'er (is this a word?).

 

[broomer5]

I run mine full when the power is off.
Shut off all return pumps.
Wait several minutes.
Fill it up to within an inch from top with new saltwater.
Good to go.
Top off 1/2 gal in the morning and 1/2 gal in the evening.

 

[rockface]

does it hurt anything if some of my bioballs are covered with water? I try, and keep my water level to where all of the balls are exposed to air. If not, I could add another 20 gal of water to my sump, and still be ok if the power goes out. I have a 300gal with a 90 gal sump.

 

[oceanjumper]

Well, I'm still a newbe but I would say that in case you have sufficient amount of LR you don't need the bioballs. So, pour in more water (at least, this is what I would do on my 72 gl tank).
On the other hand, since you have such a large tank (300 gl), the additonal 10 gl of water doesn't make a big difference in your system I would think...
If I where you, I would really focus on why, and for what purpose, you have the sump (filtration, more water, equipment hideout etc.). I would suggest you base your decision on that.