Golfish tank has white crust growing on top

Question
I have a 10 gallon aquarium with 5 common goldfish in it.  Over the past few months I have noticed a white crust on the top and where the lid sets on the tank. My tank has an aeration bar, as well as a filter which we rinse regularly. We only feed what the fish can eat, and we feed the one sucker fish in the evening one part of a wafer. What might be the cause of such a white flakey crust, I hope you can tell me.    Sincerely-Richard-Lost in Texas

Answer
Dear Richard,
The simple answer to your question about the white flakey crust on the top lid is due to mineral deposits.
This is caused by having hard tap or well water, which simply means water that has lots of dissolved minerals. There is not need to alter or change your water chemistry as this can really harm your goldfish. The best remedy is a good cleaning about once a week. Hopefully you are doing large water changes on your a bit small aquarium with high waste producing goldfish. I would at the very least do 50% once or twice a week depending upon their size. (remember to always make the replacement water equal in temperature to that of your aquarium and insure it is dechlorinated with a good water conditioner) They would really do much better in an bigger aquarium or even better yet a medium/large size pond.

Most hard water deposits can be removed by a wet paper towel or even an aquarium algae scrubber. Tougher spots can be removed by using a small razor blade (Please be careful though!!!)
Airstones are a big cause of mineral deposits because as they send air bubbles up, they pop at the surface and splash tiny amounts of water underneath the cover. (Kind of like a soda does when first popped open)

Sounds like you really know the basics of good fishkeeping and I really hope this helps!
Only my very best wishes!
Karen~