Koi suddenly died

[Sushi Prohibited]

My 4,500 gallon pond has been established for 16 years. I had 9 koi (6 at 15 years and 3 at 5 years). Last November one of the older koi suddenly died. No sign of ill health, nothing unusual on this body, no odd behavior. First time something like this happened.

Today, one of the 5 year olds suddenly died. Same thing, nothing unusual.

Does this happen? Any suggestions?

It's still very cold in Oregon, they are still hibernating, and the pond has the usual, annual string algae everywhere.

Thanks.

 

[WaterGardener]

Have you test your water parameters?

That would be the first thing I would do.

 

[WaterGardener]

Sorry. Should be tested.

 

[Sushi Prohibited]

Water looks good:
PH 6.0
Nitrate NO2 0ppm
Phosphate PO4 0ppm
Ammonia NH3/NH4 0
GH -3° dH

Any other ideas?
Thanks!

 

[WaterGardener]

Your pH is acidic, too low.

Do you have a reading for nitrite?

 

[Sushi Prohibited]

Nitrate is 0ppm.
Would the low pH kill a fish?

 

[j.w]

Nitrite not Nitrate, 2 different things.

 

[WaterGardener]

Yes, low pH can stress the fish enough to kill it. That stress can also prevent the fish from being able to fight off some other problem, like an infection or disease.

It's also difficult for your beneficial bacteria to grow well in acidic water.

 

[Sushi Prohibited]

Nitrate and Nitrite are both 0
KH is 40
GH is 30
Water temperature is 45.

Thanks for your help!

 

[WaterGardener]

You can use plain old baking soda. I'm sure it's cheaper than what you are using. Just raise the pH gradually so you don't add more stress to the fish.

Also, your KH is low. It should be around 100. Baking soda will raise that, too.

I don't know anything about the pH Up, so I don't know if it will raise KH.

 

[Laaf]

Sometimes fish just die unexpectedly. I am sorry for your loss. Yes it is worth double checking if there is anything you can fix. But if other fish are fine, that one fish may have just reached its expiration date.

 

[Lisak1]

I'd be curious to know what your pH has been prior to this? Why would it drop into a dangerous range? Did you refill the pond recently?

 

[WaterGardener]

If there is not enough KH in the system, the pH can drop. That's the reason that KH should be regularly monitored and occasionally boosted.

The nitrogen cycle, which is continuous 24/7, 365 days a year, produces acid. So if there is not enough buffer, KH, the pH drops.

Also, rain tends to be acidic, at least where I live and that can affect the pH.

 

[Sushi Prohibited]

We get a lot of rain in Oregon.

How much baking soda should I put in my 4,500 gallon pond to raise the KH and the pH?

How often should I monitor?

Thank you all!

 

[WaterGardener]

Lots of info online about this online and on this site, too. Just do it gradually and raise the pH over several days.

I try to keep the KH in my pond at 200 ppm. Having even more is not a problem. The pH is 8.3, which is fine.

I don't check mine regularly, maybe every couple of months and my pond is well established by now so I tend to slack off some. I keep a large amount of buffering with that 200, so the KH doesn't fall very quickly.