Neutralizer stone
 

Would this be safe or even necessary in a gold fish tank?

Those neutralizer stones are a bit of a gimick. The best thing for a goldfish tank is a really big filter that you rinse/replace the media often. Rinse 50% of the media, replace the other 50% once per week. Goldfish are poo-makers.

I agree. Do a 15% water change (don't forget the dechlorinator) every other day for a week, and then a 20-40% water change weekly, in addition to having a good filter. I like a 50gallon filter or two 20 gallon filters for a 10 gallon tank for goldfish. I have one submersible one, and one that hangs over the edge, to also stir the surface of the aquarium (oxygenation).

What kind of filter do you have? A submersible? One that hangs on the edge? An gravel filter?

Neutralizer
 

I have a filter that hangs on the edge in a long 15 gal tank and do water changes weekly. The well water is very hard so add Aquaplus every month but was wondering if a neutralizer would help with the hard chemicals, thanks.

Goldfish do fine in hard, high pH water.

What is your pH, gH, and kH? Most likely anything you add to neutralize the water, if you have hard water, is only causing a temporary drop in pH, and it will rise back up to the normal pH pretty quick.

A neutralizer shouldn't be necessarily unless you have extremely hard water with a VERY high pH, which isn't likely. Your fish are better off with stable water perimeters than trying to change the pH to fit what you assume the fish need.