i am not close to a sams club but i do have a bioguard product called stabilzer 100 that i used before i found this forum. it is 100%cya. but i probably only have maybe 2 pounds. according to the label, adding 1 pound per 4,000 gallons will add 30 ppm of cya. do u think adding this much would be sufficient and get a reading before adding more? i have read on this forum to be careful about getting a high cya reading...and i dont trust myself in that i got a zero results. (but the dot never disappeared). it will be tomorrow evening before i can add this product. please advise as to whether i should proceed with this product and if 2 lbs is enough to start with. thank u for ur help!!!