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post #96 of (permalink) Old 02-23-2013, 03:05 AM
Join Date: Nov 2012
Location: Portland, Oregon
Posts: 4
STS Giving a False KH Reading?

Originally Posted by Seattle_Aquarist View Post
Hi Diana,

I realize that baking soda will raise the dKH, and I use an online calculator to determine the amount of baking soda to add to accomplish the desired change.

How were you able to determine the dGH (General / German) change that would occur by adding the two tablespoons of baking soda?
I recently set up a planted tank with STS. This stuff is awesome and I want to thank everyone for the valuable information here.

Here's my issue: After 1 week with the STS tank set up, I decided to test the KH while testing the cycle progress (adding food, planted, fishless with seed media). The tap water I use measures 1dKH. I was expecting my tank to measure the equivalent or less considering that the STS might have absorbed the KH and I have not added any KH buffers. On the contrary, I could not, no matter how many drops added to the vile, get the test liquid to change from yellow to blue... At this, I performed a 50% water change and then ran the KH test again. This time it changed blue on the first drop, as did the tap water.

Out of curiosity, I took some fresh STS out of the bag and put it in a small container, added water, rinsed it, and added water and let it settle, so the water was clear. After approximately 5 minutes, I tested to KH. Again, I could not get the liquid to turn from yellow to blue. Side by side I tested the tap water without STS and it still measured 1dKH. Surely, the STS can't be increasing the dKH to 30++ (I gave up adding drops) immediately after adding it to the water! It's supposed to be inert right? If anything it should decrease the KH... I thought...

Lastly, I had some API 5 in 1 test strips handy and tried that. With this the KH square tested the same from both the tap water and the water with the STS in it. ~20-30ppm (as inaccurate as the strips are they were, at least, matching). This result lead me to believe that KH in the STS water is not affected, rather the liquid test was somehow affected.

My STS tank is at school, so I have to wait until Monday to test the KH again since that 50% water change today. I am really curious to see if the KH will still read 1dKH as it did immediately following the water change, or if the test will continue to be flawed somehow after 2 days time.

I thought I'd put this out there to see if anyone else has experienced the phenomenon with STS and the API liquid KH test.

Any ideas? Thanks for your time
TylerD is offline  
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