Well that depends on how large they are, and if you want them to go full marine yet. They can deal with it just fine, but it really isn't needed until they reach adult hood. At present you are at the high end of brackish adding any more salt is going to start to move your tank over to marine as far as the SG goes.
If that is the ultimate goal here you should only increase it by about .05 over the course of about 3 weeks to a month until you hit the full marine mark. If memory servs me correctly this is in the ball park of 1.21-1.25.
Also you should note that at full grown (6 inches) you most likely will not be able to keep more than 1 in the tank, let alone any other type of fish.
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