Need help with Algae


New member
Nov 6, 2020
Tucson Arizona
DeniseN59 I am new to your site and need help clearing a green algae overgrowth from a 1972 plaster pool with 22K gallons of hard water. I have been balancing the pool chemicals for 15 years and this is our first green algae problem.
I took a sample to pool store to be analyzed, here are the results: FC =11.8, TC=11.8, ph =7.2, Total alk =130, Calcium Hardness = 819, CYA =99, phos.= 29, TDS = 5000. We have received the TF-100 test kit and are getting unusual readings: Total chlorine color was ORANGE, not yellow. Free chlorine level was not readable, because the pink liquid only turned darker pink instead of clear. The CYA level was 100+ and the calcium hardness level wasn't readable. I have been trying to SLAM the pool water with Sodium Hypochlorite 10%. My husband does NOT want to drain the pool, according to the CYA chart, I need to SLAM at 39 ppm with the liquid chlorine. How do I test for such a high level of FC ? I am so frustrated right now !! HELP !!


Gold Supporter
May 20, 2020
Katy TX
Welcome to TFP. So happy you found this forum and that you have already received your TF-100 test kit.
With both a high CYA and Calcium Hardness, the only way to reduce each of them is to drain water. Have you had the opportunity to test your fill water? That will tell you how much CH you are adding back to the pool. There is no CYA in fresh water.
Not sure I understand the issue with testing FC using TF-100 kit. Once you add the powder to your sample it should turn pink (since you have about a FC of 12 based on pool store results). Ensure you are using the 10ml sample, thus you should add about 24 drops (R-0871) to see it go colorless. This is just estimating based on your pool store test - your TF-100 test will be more accurate. It may go colorless more or less around the 24 drop valve but be watchful as pool store results cannot be considered reliable either.
Also it is recommended to do a dilution method to test your CYA (using TF-100) since you cannot be sure how high above 100 is your real CYA level. Rather than adding 15ml of pool water, add only 7.5ml and then 7.5ml of tap or distilled water. Then add in the 15ml of R-0013 solution. Do your measurement and when the black dot disappears round up the the next level i.e. if between 50 & 60 say it is then 60. Now double 60 which is 120. That is your estimated CYA level. I say estimated because you have diluted the sample thus it creates some estimation of your level. Perfectly acceptable until you can get CYA down to under 100 and really target 40-50 level. But it provides a better understanding of your value and helps estimate how much water to drain.
Keep us updated as you do more tests.