freeradical

Thank you for all the feedback.

Correction and update: Should have stated calcium hardness=140 ppm and not total hardness. Current values: T 96.8 pH 7.7 TA 70 FC 2.0 CC 0 Borates 48 CSI -0.12 Parameters appear better to me. Is pH of 7.7 OK? My manual suggests 7.4 to 7.6 range. Since I occasionally use MPS prior to longer soaks, pH will likely drop anyway requiring periodic alkalinity adjustments. How soon after adding sodium hypochlorite do you recheck to FC level to make sure that pool calculator did not over or underestimate the required amount?

When I ran your numbers via the Pool Calculator and assumed 2/3 of the Total Hardness to be Calcium Hardness (94 ppm) the CSI reports -.62 I don't have useful experience tweaking fiberglass spa chemistry but it seems evident that in addition to increasing pH level to 7.8 or so, a modest increase to calcium may be beneficial. I'd probably increase alkalinity from 50 to 60 ppm and add a couple of ounces of calcium chloride to raise CH from 94 ppm (est.) to 120 ppm. But perhaps QCD and other spa owners here feel that the CSI is best left in negative territory and TA very low in order to keep pH stable.

Hello, I have had stable values for pH/TA for about a week and a half in a 500g spa. Last night's values follow: T set at 97 pH 7.5 (range has been 7.5/7.6, possibly due to interpreter error) TA 50 stable Total Hardness 140 FC 4.0 CC < or 0.5 CYA ~27 ppm (based on 3.36 oz dichlor added since water replacement); have switched to sodium hypochlorite now Borates ~ 48 ppm CSI currently about -0.47 by pool calculator. Should I add more calcium chloride now to improve CSI or just leave it at its current level to help prevent foaming given the spa is fiberglass? Thank you for your help.

ChemGeek, Today's values follow. T 96.9 pH 7.5 (has been 7.5/7.6 since last post) TA 50 (no change since last post) Total Hardness 140 FC 3.0 CC 0 CYA ~ 25.7 ppm (based on 3.19 oz dichlor added thus far since water replacement); no Na Hypochlorite used yet. CSI currently about -0.47 by pool calculator. Time for more calcium chloride to improve CSI? Thanks for your input.

Thanks for the info, Chemgeek. I'll just keeping checking the pH / TA for a while.

Today's first values: T 97 pH 7.7 FC 3 TA 70 CH 140 Tried to adjust pH down. TA inc. to 100 w/ baking soda. (Yes, I knew this would inc. pH but was erroneously thinking I needed to compensate for buffer loss incurred when adding dry acid.) Added dry acid to drop pH to ~7.2 while aerating spa. Let continue to aerate for 30 - 45 min and rechecked: T 104 pH 7.7 TA 50 FC 2 CC < or = 0.5 CH 140 Right back where I started except loss of TA. BTW have ozonator and added borates to 48 ppm last week. Added 3 tsp (0.5 oz) to increase FC from 2 to 6 and 30 min later, FC=10? Used pool calculator to determine value. Why the big increase? Did I check too soon? Also, do I need to go ahead and adjust CH to higher level (~200) or should I see if values stabilize first? Thanks again.

Given the general rule for requirment of 7 ppm FC/person/hour from Nitros approach, does this mean that 1 person could use the spa for approximately 20 minutes (2/7 person-hours = approximately 1/3 hour given 1 person using the tub) before the FC goes to zero? So you would have to exit the spa after only 20 minutes for 1 person, 10 min for 2 people, 6.67 min for 3 people, etc. and then add more chlorine? This is assuming that no MPS was added prior to entering the tub which would somewhat relieve the chlorine of any oxidation "duties" and allow it to be used for sanitation. Maybe I am confusing oxidation/sanitation requirements and this is leading to faulty logic. Can anyone help?

Chem geek, Thank you for the information. Couple of questions: can the pool stores equipment accuracy vary to the degree it did with my home readings if they do not perform proper calibration? Also, do you happen to have a graph of a free chlorine degradation curve for your own or another pool? I am curious about how a "typical" spa free chlorine degradation graph would look. It would be zero order, correct?

Hi Polyvue. I listed calcium hardness as "TH" above for total hardness level which is around 140-150. Using acid demand test requirements as an endpoint, added 1 oz sodium bisulfate in two doses. Last readings 27 hours after the free chlorine level of 14 follow: pH 7.6 TA 70 FC 8.8 (avg of 8.5 and 9) CC 0-0.5 Borates 48 (if calculated correctly) CSI -0.13 I did use the 10 mL sample. Also, I have neither added MPS nor used the spa since refilling. Looks like everything is stabilizing. Will consider slight adjustment of TA to 90. Should be ready to use today. Chlorine demand ≅ 37% over 24 hours. Thanks.

Recheck 9:45 am today: T97.1, pH ≥ 8.0 w/ acid demand stable at 4 drops to reach pH 7.6, TA 90, FC 11.0, CC 0.5 BTW, I have an ozonator. Had 3 ppm drop / 15 hours. This extrapolates to ~ 5 ppm over 24 hours, if degradation curve linear, yielding a chlorine demand of approximately 35% [1-(9/14)]. At this point, should I just go ahead and add the acid required as calculated by the acid demand test?

Well, I have emptied and decontaminated the spa using nitro's decontamination procedure in combination with the decontamination procedure from Hot Springs. Refilled the spa yesterday with filtered water and balanced the water: pH 7.6 (after adding 1.25 dry acid to correct a pH > or = to 8.0); interestingly, pool store "pinpoint analysis" meter measured 7.6 and they rec. 1/2 oz acid which did not budge the pH TA 70 TH 140-150 (pool store said 183- >20% difference) Added Nature2 cartridge and shocked with dichlor as recommended by nature2 instructions (1.5 Tbls/250gallons)= used 3 Tbls (1.5 oz) since I have 500 g spa. Tried to check FC 30 min later, but ran out of titrating agent. Should have been ~13 by pool calculator. This afternoon, I added 20 oz Proteam Gentle Spa (~48-49 ppm borates) around 4 pm. At 6:30 pm (23.5 hours after superchlorinating and 2.5 hours after adding borates), T= 97.8 pH > or = 8.0 with acid demand of 4 by Taylor test kit (requiring 2.47 oz 93.2% Na Bisulfate to correct to pH 7.6) FC 14 (perhaps I added 3 oz dichlor? I doubt this.) CC 0.5 (why not 0?) TA now up to 90 Will recheck FC in 24 hours to determine chlorine demand. Any additional suggestions for pH management, etc? I would like to confirm that I added the correct amount of Gentle Spa as well: Using the following post by chemgeek as a guide, I added 20 oz by volume to get to 48 ppm by the pool calculator selecting boric acid in the drop down selection box. By bottle directions, would add 13.3 oz (500 g pool), but bottle doesn't state the ppm this would yield. The MSDS for the Gentle Spa product only lists Sodium tetraborate pentahydrate as an ingredient + "proprietary ingredients." If this ingredient selected using pool calculator, 12 oz calculated to reach 50 ppm borates. http://www.poolspaforum.com/forum/index.php?showtopic=24321&st=0&p=104706&hl=gentle%20spa&fromsearch=1entry104706 "QUOTE (DubyaB @ Mar 28 2010, 07:56 PM) <{POST_SNAPBACK}> Ya I had the borates in. Not totally sure though at what level. I put 2 cups of Borax in at the water change but not positive on what ppm that would have given me in 360 gallons. 2 cups of boric acid (Proteam Gentle Spa) in 360 gallons would be 52 ppm borates so right on the money! If you used 20 Mule Team Borax instead (with associated Muriatic Acid), then that would have been 39 ppm borates. The Pool Calculator will give you dosages and near the bottom the "Effects of adding chemicals". Just make sure you enter in your spa volume properly near the top. "

I used dichlor because I will be changing the water soon anyway and was not too concerned with having it rise too fast. I have heard mixed things about bleach. I have read yours and Nitro's info re: dichlor then bleach method which makes good sense to me. I have had some people at the local dealer tell me to use bleach initially to activate the nature2 cartridge. I have had others say never use any bleach because it is "too strong." My owner's manual says never to use any nonstabilized liquid chlorine product and that it would affect the warranty coverage for the spa. The manufacturer's customer rep says never to use any bleach (she did not know what sodium hypochlorite was) because it is not strong enough- actually said because it is 6% concentration that I would have to use "6 gallons" to get the FC to the proper level! I am so tired of the misinformation and misguidance in this industry. Would love to talk to someone directly in my area that actually understands the chemistry behind the methods (as you do) as I have a science background.

Hello, I've had 500g spa since mid Feb '10 using Nature2 + MPS + dichlor shock prn. Follow Nature2 directions w/MPS testing prior to tub use + 1 oz/person-hour use time on exiting. Have had some skin changes (but no other spa user has had this) which may or may not be related to the spa, so I decided to shock w/ dichlor. CYA previously tested approx. 70 by visual cloudiness test. Poolcalculator.com recommended 2 oz dichlor in order to shock to 20 ppm given CYA level. FC was 33 ppm 30 min after adding dichlor + circulation. 24h later, level dropped to 1.4 by FAS-DPD test. Pool store then tested water w/ FC @ 0.5 ppm and CYA at 41 ppm by pinpoint analysis system. Should I keep adding dichlor until I get a more normal FC degradation time (in case there is something in the water that should not be there)? Or, maybe I should just wash the filters, clean the spa and refill it. I am due for 4mo recommended water change in mid June. Thanks for your help.

I think I will stick N2+MPS+weekly Dichlor on an as needed basis. Will likely switch to dichlor-then-bleach at next refill. Thank you again.