Hiya,
Moms got two
Small one for goldfish n young koi fry
Large ones pure koi only (bro's domain)
Built sisters koi in 97 i thinks
8ft deep ina kinda kidney shaped and width approx 12ft and length approx 22ft, She built filtration system to her specs (against my knowledge/advice so now its 6ft deep weed pond lmao)
When i was landscaping in mid 80's i did a koi pool for special order 55ft length and 35ft wide kinda egg shaped, Damn beauty when it was stocked, Guy had money to burn n spent tens of thousands stocking, eg went all over world n ordered main fish
Went back just before he moved about 1990 time to a larger place (he had 2 rear gardens for pools 100ft square and a whole 6 acre meadow at rear lol)
Fish were very large n handfeedable
Idea for your pool. Nice realisticly built cascade/waterfall be neat, Maybe in such a feature a basic bio filter
Mom spent loads on a massive 3 bed inline filter, Still to be installed cause of my pigheaded bro (all fibreglass so will keep i bet)
Once you get a pond/pool bug ya know you becoma addicted to enlarging them
lol few yrs down the line i bet ya got a nice koi setup
Guy over from a place i lived at wanted sauna and raised patio, I did him some drawings and to this day he has 50% of water under a wooden raised patio, Ideal with vegatation in for spawning etc and fish have a real large pool
Real nice on summer nights supping a few bevvies and hearing koi gulp feeding and a trickle of a very large waterfall he did
Feel relaxed near waterfalls etc wanna know why ? apparantly it the water friction giving off some kinda chemical-type-thing (did know word but mems shafted)
Well keep on i sure you'll all love the finished article
EDIT: rich koi dude had a grey tall bird visit a few times after stocking, 4am on a summer dawning it ran outa look on the poaching koi side o things and ended up in a mass of feather, Funnily he said he heard 2 12 gauges go off at the same time
Of course it wasn't him protecting his valuable fish, Must of been a guardian koi-pool angel
Here them pesky grey birds are protected somewhat