Wow 800 PPM. A water filter will really help, thing is with water that dirty you will want to have replacement filters on hand. Perhaps even put a large sediment filter in before the RO filter to help.
When the prefilters get dirty the unit will really slow down on production.
When the output PPM starts to rise the membrane is bad. I always replace post filters when I change the membrane.
I always have to replace the prefilters about 2 times before I need to change the membrane on the third. My tap is about 245 PPM. since you have 800 PPM you may have to change prefilters more times before the membrane is bad.
If you have low water pressure you may want an
electric booster pump or a
permeate booster pump.
You can setup a barrel with a drain valve in the lower side, set it on some cinder blocks. Put a float valve in the top side that is connected to the RO output. This barrel can then be used to store a bunch of filtered water. Toss a water pump in there to circulate the water, even provide a waterfall if you want to get it nice and oxygenated. Air stones will warm the water more and can cause pH flux.