I did say Siphon it In a bigger tank you can permanently install the syphon access in the back ground so you don't have to dig out the soil to do it, or you can drill the tank at the max waterline and install a bulkhead so the water drains out as needed.

You frog is likely stressed out. Let him/her be for a bit and get use to the changes. By a bit I mean a day or more. Your cobalt will calm down and start to explore.