Some observations resulting from my belief I had a pool leak!
I have an in-ground fiberglass sports pool in central Florida that is 24 feet long and 16 feet wide. At one end is a jacuzzi, the top of which is approximately four feet above the pool deck level, with a waterfall lip into the pool. A pair of 3-way valves at the pump allows me to shift suction variably between the jacuzzi drain or the pool's skimmer and drains, and to shift return flow between the jacuzzi jets and the four pool inlets. The only control method to regulate suction between the skimmer and main drain in the pool for running the pool vacuum is by blocking one of the two holes at the bottom of the skimmer - not how I would have designed it! The pad with the Hayward pump and cartridge filter is approximately one foot higher than the pool inlets, and two feet below the jacuzzi inlets. Additionally there are two valves accessible at the jacuzzi, one to close off the jacuzzi drain line back to the pump, and one to close off the inlets to the jacuzzi from the pump. I found the drain valve closed, inlet valve open, and leave them that way.
The previous occupant had drained it (as for why, let's not even get into that crazy mess except to say that divorce situations can make some people behave insanely!) and it was an algae dump when I arrived. After fully draining, pressure washing and refilling the pool, I thought I may have a leak as the water level was dropping as much as 1 1/2 inches or slightly more in a week, higher than I would expected from estimating evaporative loss alone. The pool is not being used as it is winter and it is unheated - brrrrrr - so splash out is not a factor! My first suspicion was a possible leak on the suction side of the filter system, since I am seeing some slight air bubbling on the two inlets closest to the pump, though none at all on the other two farthest from it. I also noted that if the 3-way return valve is left partially or more open to the jacuzzi inlets, within an hour or two of the pump stopping, the water level in the jacuzzi drops to the level of the inlets - I surmised this is caused by backflow of the higher level jacuzzi water through the system to the pool inlets, and does not occur if I close the line to the jacuzzi inlets. One possible leak source seemingly eliminated?
My next testing involved running the system for one week without any feed to the jacuzzi, returning filtered water to the pool only. Water level drop was right about 3/4 of an inch. The next week, I ran the system with full return to jacuzzi only for max waterfall flow. Water level drop was just over 1 1/2 inches. This leads me to believe that either the waterfall causes a significant rise in evaporative losses, or I may haver a leak underground in the return lines to the jacuzzi.
Anyone with experience in waterfalls and their effect on evaporative losses out there care to comment on this?