My check gauges light comes on, and the water level goes down and then goes right back up to normal,and the gauge light goes off this happens when I slow down.

What water level?
What kind of car?

https://www.askmehelpdesk.com/cars-t...le-303903.html

Read your Owner's Manual on how to drain and refill the cooling system. Follow their instructions precisely. There may be air in the system or there may be a problem with the coolant level sensor in the reservoir. It's not uncommon for these sensors to come on and incorrectly signal the coolant level is low. If this is the problem, either add additional coolant slightly above the full line, install a new reservoir, or simply disconnect the connector to the sensor and watch the level yourself.