I am quite new at the hobby, but I think I can help you out ... someone please correct me if I am wrong.
I would replace the "T" with an air control valve (3 way) ... here is an example of what I mean:
http://www.hagen.com/canada/english/...01011790010101
This wil allow you to control the amount of air that goes to the ornament and the airstone, it will only take a few minutes to find the correct balance. Also, the 3rd valve should be left open just a "tiny bit" to decrease the pressure applied against the diaphram of the pump ... it doesn't take much, just a very small leak of air from the 3rd valve to prolong the life of the pump. Having said that, it's a good idea to have a repair kit for the pump just in case.
One other thing, I would spend the $3.00 and install a check valve (
http://www.hagen.com/canada/english/...01011650010101 ) between the pump and 3 way valve, that way water can not make its way back to the pump and ruin it.
That's my 5 cents ... hope it helps!
Moe