Why would I have used washing soda in the past?

[watson524]

Hi there,

After a few years of not using it and moving (tub was drained etc) we are firing it back up now that we were able to source the 60a spa panel and breaker we needed for the outside disconnect. Filled it, ran ahhsome, draining now, then willl refill and start the balancing. I'm revisiting old threads to jog my memory but also reviewing my old log book from the last fill.

I had to add some calcium boost (well water at old and new house) so not surprising. I got that set and had an initial TA of 80. Added muriatic acid and started the check of the TA/pH after aeration. One of my next log entries is that the pH went less than 7 and then I added 1.15oz washing soda and got to 7.0 and then added another 1oz of washing soda and got the pH to 7.8 then did the dance of adding MA, check pH/TA, add a little more acid etc.

I canNOT remember why I would have put the washing soda in and don't see it here How do I use Chlorine in my Spa (or pool)? (tho I see baking soda so sodium carb vs bicarb). Was the washing soda because pH was TOO low after my initial muriatic acid add and I needed to get it back up? Seems like it from my log but wanted to confirm.

thanks!

 

[mknauss]

Baking Soda = big TA change, small pH change
Borax = Big pH change, small TA change
Washing Soda = big pH change, big TA change. Probably more TA change than you want.

 

[watson524]

huh, reading the log, started at TA of 80, after the calcium boost (3oz) to take CH from 80 to 110 but the pH over 8.0, the 5oz MA plummeted the pH to under 7 but adding the washing soda got it to 7.8 and the TA before I started dialing it in read 90 so it didn't seem to do TOO much to the TA.

 

[CuckooChris]

5oz of MA is a lot. I only add it by the tablespoon. I don't worry about the TA much, only the PH. When PH gets up near 8, add a Tbsp of MA. TA is usually 40-50 when I occasionally check it. I would check your PH after it's full and if it's in range, don't add anything.

 

[jseyfert3]

huh, reading the log, started at TA of 80, after the calcium boost (3oz) to take CH from 80 to 110 but the pH over 8.0, the 5oz MA plummeted the pH to under 7 but adding the washing soda got it to 7.8 and the TA before I started dialing it in read 90 so it didn't seem to do TOO much to the TA.

On a 500 gallon tub, 5 oz of 31% acid will drop the TA by 39, or if you're using half strength acid by half of that. 2.12 oz of washing soda then would add 30 TA. So basically you just restored roughly all the TA the acid ate up.

The only time I've used washing soda was when I overshot my acid additions, and tanked the pH. Now I try to be more careful, especially when my TA is sub-100.