Auto Top off (Fail safes)

[Nemain]

I have a float switch in sump that triggers a pump in a container of RO to top off sump.

Is there:

a) A way to ensure the pump in the container of RO doesnt run dry;
b) A way to ensure my sump isnt flooded with fresh water

I really need something EXTREMELY easy to comprehend and set up.

I hope this is more clear this time.. I was mixing up my oilfield jargon with my fish jargon :P

Beth