The most important piece of equipment these days in the koi world all ways quarantine your koi when you buy from someone you have never dealt with before ,quarantine your koi for at least 3-4 week with in this time you can keep a close eye on it, also take regular scrapes of your new koi and watch out for any flashing or jumping this normally indicates a parasite problem
by adding heat to your quarantine system this could bring out any unforeseen problems also can be used for bringing on small koi and don't forget to net the top of your tank,use a fine black net this helps you see the your new or injured koi better,
When medications and water treatments are added koi will get a bit agitated and may jump.
Always quarantine new fish.
Never introduce them to your existing fish until after a quarantine period of 2 to 3 weeks,
longer if possible.
Always treat new fish as if they have parasites, viral, fungal, and or bacterial infections.
Better to be safe than sorry.It is also possible that your existing fish have parasites, viral,
fungal and or bacterial infections. They may have built up a tolerance, while the new arrivals
having undergone the stress of shipment could succumb immediately.