Do I calculate display tank gallons + sump gallons for...

[TurboTimmy]

Hi everyone! This might be a silly question, however, I've never ran a sump before and want to make sure I do this correctly.

Would I be accurate in stating, given that I have a 90 gallon display tank, and a 30 gallon sump, when adding chemicals or shopping for a protein skimmer...I do for a 120 gallons?

A little more complexity, I have 100lbs of live rock (pic does not reflect all 100lbs in there) so do not actually have 90 gallons of water in the display tank. Regarding a protein skimmer and if my above statement is correct, do I actually need one 120 gallon capable?

I ask because I am having trouble finding a 120g capable one (on Amazon at least) that is short enough to fit in my setup.

 

[edd59]

a 90 gal doesnt even hold 90 gal. its calculated from outside dimentions.
and your sump might only be filled halfway. you might have 90 gal total water in reality.

 

[19Mateo83]

@IOAOI has some rated for 100 gallons.

https://a.co/d/7f2TTju

 

[cilyjr]

When dosing a chemical, you will want to find out how much actual water you have. This is because water chemistry is taking into account exactly how many gallons of water there is.

When equipment sizing the manufacturer is usually talking about the size of the tank.

 

[Daenion]

I would take at least 20% off the total volume when calculating.

 

[piranhaman00]

I always create a solution of KNo3 and dose the tank and back calculate my true gallo s