My 2015 is losing coolant, mpg is dropping

Opened my closed block tester package and the fluid, while supposed to be blue, had a blue greenish tint to it. It states that it turns yellow in presence of combustion gas. But it says if the fluid is green to start, it's no good according to instructions. So I went ahead with the test anyway, and it turned from blue green to blue. I tested it quite thoroughly. I don't have any obvious rough idling or death rattle in my 2015 Prius. I think what I'm going to do is push some exhaust fluid through this tomorrow and see if it turns yellow. In which case I'd conclude that I don't have a gasket leak. It's a big drive across my city to get another bottle of the tester fluid.

Basically, I'm slowly losing coolant and mileage has dropped. But I have a few things to do early next week:

1. Replace water pump (after the head gasket, next place to look for a leak). I got a kit to replace the innards of the water pump off Amazon. Youtube instructions on this. Will also replace thermostat while I'm at it.
   
   
2. Replace EGR valve, clean Exhaust intake. (Relying totally on Youtube here. Don't know at all what I'm doing)
   
   
3. PVC valve replacement
   
   
4. Clean fan system/ventilation to battery (may be overheating in this heat).
   

.I've got two different problems that are not directly related. First is the loss of coolant, and second is the drop in mileage. Any other ideas, I'm happy to hear. My skill level in auto repair is about a 2 out of 10.

 

190k.

 

I am still determining what sort of timeframe this is over. It was noticed during an oil change yesterday, so I figure doing the other things worthwhile. I think head gasket replacement should be about 2k locally. It's never thrown any error code. If I do the other stuff and it continues to lose coolant, I'll get the head gasket replaced. Hoping to drive this car several more years. I love it, even though it's almost 10 years old.

I actually bought a boroscope. Is there a youtube video I should look at, or do I need to take it somewhere else?