Thanks Micheal.
The way I figure it, this Glass Cages 190 rimless holds a lot less then 190 gallons.
The tank is 48"x36"x24" and those external dimensions equal the 190 gallons.
However the glass is 3/4" thick all the way around so that has to be subtracted.
Its not filled all the way to the top so that has to be subtracted.
It has reef ceramics, live rocks, sand, and 2 Streams and a Wavebox so that has to be subtracted.
Probably at least 25% or more of the 190 gallon rating on the tank is not water but I do have a 20 gallon sump however.
I'll report back after I get the PTC running. Worst case I'll just have to get another PTC 6( of course I would want to add to the system volume if I do that)!
James