Young koi in trouble, please advise

[coolwon]

Maybe too little air.
Scramble the surface water
No dead spots in tank

[Summer]

BIG water changes. - Are you neutralizing the chlorine?

Growth. Do you have lots of air through stones turning the surface water over?

Garfield

I ALWAYS use Prime with every water change and match the temperature.
I have one air stone bubbling to the surface in each tank and the return jets near the surface in each tank.
Do you think that too little or too much air could be affecting growth?

Thank you for replying!

[coolwon]

BIG water changes. - Are you neutralizing the chlorine?

Growth. Do you have lots of air through stones turning the surface water over?

Garfield

[Summer]

I have been a koi enthusiast for 6 years. My pond is 10k g, 6' depth. Stock 17 koi.

This year in April two of my koi spawned and I decided to try raising about 800 fry, for fun (Ha Ha)!
I had no idea how much work it would be! That said, I have loved the experience!!!

Until now, the only problem I've had is that they haven't come close to growing according to scale.
They are not skinny, or fat, and there is a huge variance in sizes, so I sort them by size in ten 100g tanks.


The problem I desperately need help with is a few weeks ago I started having fry go upside down! I've scoured the Internet, my koi library, talked to local fish stores and tried peas, salt, and a variety of treatments on the afflicted fish, but nothing has stopped the condition from occurring or corrected it in the afflicted fish. The koi look perfect, no lesions, fungus, visible parasites (I bought a microscope), or anything abnormal. Once they lose buoyancy or the ability to right themselves, they continue eating and live for several weeks, but never regain control. Some after improved after warning their water and salting, but they usually relapse and eventually I lose them.

Please offer ANY advice that might help them and me figure this out. It's taken 30-40 beautiful babies over the last month and I am desperate to stop it.

Water changes 30% every fourth day, Nitrite 0 ppm, Ammonia 0 ppm, Nitrate 5-30 ppm, pH 7.8

Sincerest thanks for any help!!!