I assuming from your question that you are referring to a high sump water level when you say " Should I install some sort of float switch to power on the pump when the water level in the sump reaches a certain depth"
There will be times when the water level in the sump will be high, such as power outages and doing normal maintenance.
On power loss - the water level will rise - and when power restored the pump will turn on and return to normal operations - no switch required.
When doing maintenance on your tank - there will be times you want to raise the level in your sump - to vacuum out detritus or doing water changes. No switch required.
Plato is correct - a float switch can be installed for low water level pump protection - you can get these from Kent Marine.
Some people do install an auto top off system that employs the use of a float switch to either operate an electic solenoid valve, and electric pump .... or to physically open an orifice valve allowing RO/DI water to be added to sump.
I've marked my sumps with colored tape to indicate 4 levels.
Top level - Sump max level at power loss.
Next level - Sump level under normal operation without skimmer running.
Next lower level - Normal operating level with skimmer running.
Bottom level - minimum level before pump damage.
Then just add top off water to keep it within near the normal levels.
When placing these colored tapes on outside of sump, do this by checking your specific gravity for "normal levels" compared to your sump design/capacity.
HTH - Brian
