I'm sorry to hear about squirt dying. The good news is that starting in October (7th and 8th) there are day time minus tides, lower than -0.5', for the next few months, so you'll have a lot of chances to find a replacement.
Do you know if Squirt was male or female? Was "he" showing signs of senility? If not, then he probably didn't die of old age, any idea what might have killed him? Any recent changes in diet, filtration, anything? I doubt if golf balls are toxic, but it's worth wondering about.
I did a little Googling and found that "surlyn" is a common material used to cover golf balls, and that some types of surlyn contain zinc. zinc is toxic to mollusks, and I wonder if this could have been a factor in Squirt's demise.