Amount of water for tank size seems low

[adicus]

I have a 75 Gallon with a 19 gallon fuge/sump combo for a total of 94 gallons. I have 123 lbs. of live rock and 90 lbs of live sand in the main tank. In the fug/sump I have a: Protein skimmer, heater, and two small pumps for UV and phosphate reactor.

I carefully measured the water when I added it and totaled only 60 Gallons. This seems low to me - anyone have an idea of the ratios? Also should I base my % of water changes on 60 Gallons or 94 Gallons?

 

[Len]

It doesn't sound too far off. Is your 19 gallon fuge/sump fully filled? 125 lbs of LR should displace over 20 gallons, so it's just about 10 gallons that's not accounted for. A 75 gallon is really more like 70 gallons (since 75 gallons is based on external dimensions, and a tank is rarely filled to the brim). There could also be other variables that effect the results. But 60-70 gallons for your system is in the right ballpark.

I would base your water changes on your actual water volume, though the ratio isn't an exact since, and doing more wouldn't hurt Knowing the actual water volume is more useful when calculating additives (and medication).