The more I read, the more I realized I don't know many things on pool chemisty.

I am still waiting for my TF100 test kit and it will not come until sometime, because it will join my other shipment within USA into Indonesia.

Anyway, I am curious about having too much CYA in my pool or better I would say that I would like to be able to predict CYA accumulation in my pool.

I am now using 90% Tri-Chlor tablet at 3" size and 250 grams per tablet ( approx 8oz )

TPF sticky mentioned that for Tri-Chlor, it will add 0.6 part CYA for every 1.0 part of chlorine it adds.

Pool calculator for Tri-Chlor stated that 1PPM of FC in my 35K pool will need 5.1 oz ( 150 grams ). I am assuming that my Tri-Chlor being a 90% strength is the same as what the Pool Calculator is using.

I don't have my pool log book with me, but I am averaging off my head at 3kg ( 100 oz ) Tri-Chlor use a month. Sometime I add Cal Hypo for shock and that does not contain CYA.

To today from March 2007 is 14 months or 42kg ( 92.4lbs ) of Tri-Chlor used. I add water at about 400 liters per day or 105 gallons. So in total my pool water including losses is 14 months x 30 days x 400 liters = 168,000 liters. Pool size is 135,000 liters, grand total is = 303,000 liters ( 80,158 gallons ).

Can I calculate like this ? :

Version 1 - Assuming 10% of my Tri-Chlor is the CYA component and 90% is the chlorine

42 kg x 10% = 4.2 kg

4.2kg of 303,000 liters = ( 4.2 / 303,000 x 1,000,000 ) = 13.86 PPM of CYA

Version 2 - Based on Pool Calculator data

If per 360 grams ( 12 oz ) of Tri-Chlor raised my CL in 303,000 liters ( 80,158 GL ) pool by 1 PPM and 0.6 of it is CYA, that means 42,000 gram chlorine used divided by 360 grams = 116 PPM of chlorine accumulated

116 PPM of chlorine equivalent been consumed in my pool that has total water contained and consumed so far at 303,000 liter ( 80,158 GL ). If 0.6 of it is CYA and that will stay in my pool, I am assuming I am now having 116PPM x 60% which is 70 PPM of CYA.

Holy cow !!!!! I hope I calculated wrong

Help-Help....

Many thanks

Surya