Hello, everyone. I have a 7 year old feeder goldfish (the kind you get at the fair), and he has one scale that has a reddish streak that looks kind of like red pest disease. He currently lives in a 55 gallon fish tank. A few days ago he suffered through a pretty traumatic event... his 60 gallon fish tank randomly blew; luckily my parents were home and were able to scoop him out and into a big laundry bin right before he ran out of water. A 55 gallon tank was all they could find at 8 pm that night when this all happened. He’s acting fine and eating well. He also doesn’t seem to mind the new tank despite it being 5 gallons smaller, but I’m not sure if stress could cause whatever is happening to his scale. He’s lost a 2 or 3 scales before (they just fell off?), but I’m worried he is sick. Since we had to get him a new tank after the last one blew, he had a complete cleaning with brand new rocks and everything. Before the accident, he would have his tank cleaned every 1 1/2-2 weeks since he is a very dirty goldfish. Please help!
Goodness! Given the trauma of the event, and your goldfish's good fortune that your parents were at home and able to save him and think quickly about where to put him until they quickly/fortunately were able to get him a new tank, it seems as though he's been lucky only to have an injured scale - so well done all round.
*However*, this is where you must now be careful for the next few weeks at least - the stress of the event, plus the damaged scale, will likely reduce his immune system, and make him more susceptible to disease such as finrot setting in.
This risk will be compounded even more with the likely mini-cycle that your tank will be undergoing (due to the loss of beneficial bacteria which process his waste - this beneficial bacteria resides in the substrate, decor, tank walls but mostly in the filter and specifically the filter media) or even full cycle that it may be undergoing (if you've had to put in a new filter and/or new filter media). It'll be very important, therefore, that you follow this guide https://www.fishkeeping.co.uk/articles ... ammonia-nitrite-spike.htm
More generally, and once the situation has settled, it's best if you can do a water change weekly (rather than every 10 days or a fortnight) - and keep ammonia and nitrite at 0 at all times (which may mean even more frequent or larger water changes).
Hope that helps but do get back to us if you have any further questions at all or if he looks as though he's getting worse. I'll keep my fingers tightly crossed for him.