Cavitation on 4R100 pump

not good, so to protect from that, go to ELC concentrate, fill with 4 gallons of ELC and then top off with distilled water?

after it is flushed clear of the previous unknown coolant, which for me is pink or yellow, can't tell, I am pastel color blind

Hydraulic cavitation is caused by air. In this case it was caused by air constantly being sucked in at the filter oring.
In other situations on other hydraulic systems, it is usually is caused by air being sucked in on the suction side of the charge pump. A charge pump typically makes a couple to a few hundred psi depending on how it was specked out for that application. An auto transmission pump is a charge pump in basic design. It however does not “ charge a high side pump of a system. In a system that does produce high pressures the charge pump “charges” the high pressure side pump. That system is used in your truck’s engine. In other applications, the charge pump is almost always in a consolidated pump unit that incorporates the charge pump and the high pressure pump all bolted together. It’s bolted to a power source be it an engine or high power electric motor. It has a port for a hose to suck on into the charge pump. The charge pump has an internal out port which is the in port to the high pressure pump. Upon exiting the internal exit port/ports, it passes by a relic valve poppet or dump valve. It is then directed to external ports for hoses that typically go to a hydraulic torque motor that converts the fluid motion and pressure into mechanical torque that can be harnessed. Air being sucked in can and will literally cut steel, aluminum and brass. Air that is on the opposite side just compresses and does not cause damage. It just makes whatever the fluid is acting upon just not operate properly.
Class dismissed for the evening. Clear and Present Danger is on TV.
I will leave you with this fact; Air is dangerous to hydraulics. Make sure it is not present. 😉

Speaking of charge pumps and all hydraulics be extremely careful. When looking for leaks in a pressurized system, always have goggles on and use a piece of cardboard. Keep you hands clear. A tiny pinhole leak maybe invisible to the naked eye. It can pierce your flesh. If it does, you are done. You have to go to the hospital. They have to do surgery in you. They cut you open to flush the oil out and sterilize. Failure to go to hospital to have this performed, you will have gangrene. That will result in something being amputated.
Never try to perform off the wall diagnostic technics. I once was working in a diesel and hydraulics shop. A tech had a New Holland skid steer with dead hydraulics. Tech came to me and asked what I thought. I said if nothing stands out to you after checking fluid level and new filter, put a gauge on the charge pump test port. Welp, He decided to ignore my instruction ( FIREABLE offense for a good reason). 3 minutes later, I hear it fire up. I think, No way does that guy have a gauge hooked up. I come from behind a truck to look. He has a rag wrapped around a blow gun shoved into the hydraulic reservoir. I screamed at him NO. He could here me over running engines. He hit the lever on that gun. It pressurized the tank forcing oil into the high pressure side of the pump. The skid steer had the neutral safety, parking brake,seat switch and seatbelt switch system bypassed by the hands of its owner. That system controls use of the engine starter and hydraulics by way of two dump valves in the pump. The right turn lever was left in the forward position because the tech was hanging onto it as he climbed out of the cab. Welp… Once the high side of the pump got that pressurized oil, that skid steer instantly pinned that tech against a cinderblock wa. I ran over and shut the engine off. He is screaming. Bunch of other techs are screaming at me to get it off of him. I said no, he might hemorrhage. He will pass out in a minute. He did. He got a flight downtown to Shock Trauma.