Amy welcome from Plymouth in the UK like you we kept aquariums for 22 years keeping our koi in a huge indoor aquarium and have been outside now for 5 years in our own pond forced to do so by health issues and have found it far easir when it comes down to maintenance due to doing so
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Had we remained indoors we would have had to give up our long time love afair with koi
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Please believe me when I tell you you have a steep learning curve ahead however if you are careful and learn the lessons well you'll become a good koi keeper.
Your first lesson is to be exact in your gallonage, a pond cannot be around 300gallons US it has to be spot on.... why ? This is because you need the exact gallonage for future treatments remember too much can overdose overdoses can damage your koi and even kill or maime them
. :-
https://www.gardenpondforum.com/thr...on-and-the-correct-use-of-in-your-pond.10512/
Your best bet is to do what we did buy a water meter and meter the water into the pond, this way you'll know just how much in the way of chemicals to treat your koi safely .:coo:
Next cycling a pond is not the same as cycling a tank , it takes longer and will go against everything you know , so dont stock your pond with koi straight away put one or two sacrificial fish in the pond to help cycle it and only when it is cycled add your koi.
Dont forget to create a QT fasiltiy (perhaps a smaller pond of 3-500 gallons) this is vitally important as you cant put large koi into small aquariums and expect them to get better
Buy books on koi keeping especially fish and koi health see our koi and fish health library thread for these :-
https://www.gardenpondforum.com/threads/our-fish-koi-health-library-with-reviews-of-each-book.10498/
Learn the use of anethetics your going to need to :-
https://www.gardenpondforum.com/threads/anethatizing-you-koi-goldfish-the-various-stages-of.10493/
Do you have a microscope your going to need one to identify potential parasites as ponds arent like aquariums in that they are open to parasites :-
https://www.gardenpondforum.com/threads/microscopes-and-scrapes.11108/
Netting koi is different to netting fish in an aquarium ;-
https://www.gardenpondforum.com/threads/catching-your-koi-netting.10579/
You can also put together a first aid kit for treating your koi as believe me when I say this your going to need one especially during spawning :-
https://www.gardenpondforum.com/threads/make-a-complete-first-aid-kit-for-koi-and-goldfish.10984/
Remember pond and filter maintenace is an absolute must on a koi pond it would be in your favour to add either one or two 4" bottom drains otherwise you will find yourself having to vacuum the bottom of the pond on a regular basis especially in fall .
Having bottom drains acctually is a very clean way of doing things as all the detritus is taken away by your bottom drains direct to filter
Remember to do reguler water changes you can negate the use of dechlorinator/dechloromines by using a special filter connected direcly to your hose pipe :-
http://www.vyair.com/scripts/prodView.asp?idproduct=67
Sorry to give you all this information in one go but it will I promise you help you to become a good koi keeper
All in all if you manage to get through the first year your onto a winner , I hope the threads weve put in our post go half way to helping you become good koi keepers or goldfish which ever you decide
Dave