mattfort Posted August 15, 2011 Report Share Posted August 15, 2011 Hi, I have a 550 gallon spa and am using a nexa spa SWCG with dead sea salts. Unfortunately, I filled and added the salts WITHOUT testing for hardness.... I'm getting a bit of foam in the tub, so I tested my hardness from the tap to see what I filled the tub with. The tap is reading next to NOTHING on the test strips. However, if I take a TH reading on the tub, it goes 1000+, because of the dead sea salts. How should I go about adding the correct amount of calcium to the tub? My thoughts were to take a 5 gallon pail and add calcium until it reaches the optimal level. Then, use that formula to harden the tub water. Would this work? Quote Link to comment Share on other sites More sharing options...
chem geek Posted August 16, 2011 Report Share Posted August 16, 2011 You can use The Pool Calculator to see that adding 120 ppm Calcium Hardness (CH) to 550 gallons of water requires 9.8 ounces weight (about 7.8 ounces volume) of calcium chloride (anhydrous) or 13 ounces weight (about 15 ounces volume) of calcium chloride dihydrate. This assumes that the reading of your tap water is correct, which is doubtful. Tap water usually has at least some hardness, though you might be in an area where that's less than 50 ppm CH. You should really get a better test kit -- the Taylor K-2006. Quote Link to comment Share on other sites More sharing options...
Mark SC Posted August 16, 2011 Report Share Posted August 16, 2011 My situation is similar. Tap water is about 40 ppm CH. I just add a little to bring it to 80 with my SWCG and have no foaming issues. Quote Link to comment Share on other sites More sharing options...
mattfort Posted August 16, 2011 Author Report Share Posted August 16, 2011 Took a sample of spa water to my local pool / spa store and they put it to the test, using a Clear Care Expert system.... FC 1.61 TC 6.03 (Yes, I shocked it earlier in the day) TA 0 ppm ph 6.5 CH 159 CYA 0 Copper 0 Iron 0 TDS 0 I added 16 oz of Alk increaser, then 16 oz of Calcium hardener..... Will take another sample and bring to them later this week, Crazy how shitty the test strips are..... Quote Link to comment Share on other sites More sharing options...
chem geek Posted August 17, 2011 Report Share Posted August 17, 2011 Whoa there. If your CH was already 159 ppm, there was no need to increase it and if you added that much Calcium Hardness increaser, then your CH is now high and you could risk scaling if your pH got too high. Right now your pH is low, but 0 ppm TA is IMPOSSIBLE if the pH is 6.5 (how did the pH get that low anyway?). The pH would have to be 4.5 or lower if the TA were truly 0. So, quite frankly, I don't trust these numbers that much better than your test strips. PLEASE get your own good test kit. This is why we ask everyone to do so. Quote Link to comment Share on other sites More sharing options...
Mark SC Posted August 23, 2011 Report Share Posted August 23, 2011 Those electronic test systems in pool stores are not always accurate. I took a sample in once and it registered 7.0 pH when I know from a drop test using two different kits that it was 7.6. Quote Link to comment Share on other sites More sharing options...
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