I like to keep the level in the reserve tank  about an inch above the min
mark when the engine is cold.   Scott

Do you have an owner's manual? It states what the level
should be.

The rule for your 94 Civic is to make sure the coolant is at
least the reservoir's low mark when the engine is cold. Then
run the engine to warm it to normal operating temperature
(so take a trip to the store or something). Turn off the
car. Then check the reservoir level again. Add coolant as
necessary to bring the coolant to the high mark.

www.autozone.com has a complete manual for your Civic that
discusses this and also air purges of the cooling system.
Air in the system can mess up your level readings, among
other things. A proper purge, using the manual's procedure,
will get rid of all the air and also top off the coolant to
the correct level.

the tank is more an "expansion tank". The coolant expands when it
heats up (like most things) and needs a place to go so it is held in
the tank until things cool down again and then it is pulled back
into the engine. So what you are seeing is normal operation of this
sytem.

Isn't the tank marked clod and hot level's?

Tom