Koi Ponds- Size- Upkeep- Watch Out For

Am Involved with real estate, and a seller had a small koi pond about 5 X 7 ft. and about 30 inches deep. This seller left for new home, and new owners did not take possession until 3 months later. I took it upon myself to feed fish every other day as i live a distance from other house.

The pumps were turned off for about a month, and the water was murky, dark brown, and one could not see beyond the surface. When I fed fish few would venture to the top, and so I remained about 10 minutes and left.

I thereafter determined to get the pump running, and after reading koi articles determined that I might be able to do water changes to get the water cleaner.

After changing water about 10% every other day, I determined there were 55 yes 55 koi living in this small pond. They were about 5 that were 10 to 20 inches, and the remaining were 5 to 8 inches.

A storm occurred here and trigs were in the pond, and a puncture in the liner occured and there was only about a foot of water remaining. I did not know if the bottom of the liner was where the tear happened, so I just kept adding water each day to keep the level up. I thought better to have some water then none at all.

Half the fish died, most the larger. The remaining fish were taken away, as I found a supplier who wanted about 25 or so of them. I took 4 small ones [about 4 to 5 inches] and they have been living in my garage for 3 months, in a 20 gallon tank.

Hearing all about space needed, and the special care required, and then seeing 55 koi live in such a small place, I'm perplexed. I'd like to have a small pond of about 180 gallons. How to keep these 4 alive on outside ? Do I need special filters, pumps, those lights that kill algae? Being on fixed income can
I find more econonically, less costly pumps, lights, etc so my electric bill is not sky high.? Any recommendations? Suggestions? name brand recommendations? Thank you. I really like to keep these guys alive.