KH value stuck at 90

[VAPondGuy]

6000 gallon pond with 17 koi.
All metrics except for KH are normal.
KH value is 90 and stuck there.
I tried adding four cups of baking soda. No change in KH.
I bought Buff-It-Up hoping that this chemistry would be more effective.
Adding 2 cups of this has not changed the KH value.
It does, however, turn the water chalky white. This color dissipates overnight.

I had a bad experience with a pond service tech who dumped calcium chloride into my pond, turning it white. A massive fish kill resulted.
So I'm afraid to keep upping the dose of Buff-It-Up for fear that I'll suffer another catastrophe.

I'd appreciate advice on why my KH is not responding to baking soda or B-I-U and whether or not I should be concerned about the chalkly water.

 

[IPA]

Are you using strips or test drops? Which kit?

 

[VAPondGuy]

Thank you for responding.
I'm using drops.
The two test bottles are shown in the attachment.

 

[BKHpondcritters]

The formula for raising kh that I've always used is 1 cup of baking soda per 1000 gallons, so for a pond of your size you would need to use 6 cups. Dissolve that amount in a bucket of pond water & add it to your system (I usually pour some in each of my two skimmers) Wait 24 hours & test again - it should bring it up 1 drop on the test kit chart. (so if you were at 5 drops, it should now be up to the 6 drop level) Repeat every 24 hours until you get to the level you want (usually anywhere between 100 - 200 is OK)

 

[IPA]

I have read 1 cup baking soda for 1,000 gallons of pond water to per day until you reach a KH value of 150.

 

[WaterGardener]

My pond is the same size as yours. I normally use 6 to 8 cups when I need to raise the KH, and I keep the KH of my pond around 200 ppm. If your pH is 8 or so, you can add as much baking soda as you want. It won't raise the pH over 8.3 so there won't be a drastic rise in the pH. If it's below 8, then you need to be more careful with the amount you add each day.

 

[VAPondGuy]

This is all very helpful.
Because baking soda doesn't cloud up the water, I'll switch to that and use the quantities you suggest.

Many thanks.

 

[Mmathis]

Try adding some crushed oyster shells — put them in a mesh bag and add them to your filter.