Don't panic. With redbugs you have time to treat without rushing.
If you do an in tank treatment, the original dosing method called for 1 tablet to treat up to 380 gallons.
Revised method has used from 5 to 10 times the concentration without problems.
The red bugs aren't supposed to lay eggs, so a one time treatment is supposed to be adequate.
Remove any crabs or shrimps that you want to keep, before treating.