I need some help with scale please !!!

[mandtra]

For the past two weeks , I have had ph bounce.  it would be 7.5 all day then we would use the spa for an hour and it would go to 8.1  or so .  this would happen every day  (have used an entire bottle of ph down in 10 days).   We have not used the tub for 3 days and now there is scale build up everywhere , everything feels very rough. esp around the jets and in corners. the water was at PH 7.7 , TA 120 , CH 170  spa is acrylic , and only two weeks old 425 gallons.     I'm using a Taylor K-2006c  test kit   and have had pool for over 10 years

What is the best way to dissolve the scale ?  is there a product i can use ?   I want to make sure the plumbing and heater is cleaned out as well .

What i have done so far.    I have lowered the ph  to 6.8   TA 80  and lowered temp to 85 degrees  & CH 150 &  Br 4.0  added a triple dose of ace brand metal out
is it true at these levels the scale will dissolve on its own 

[Jacuzzi Jim]

 Bout the only thing you can do is drop the PH/ALK to 0  that will convert the calcium back from a solid state for a lack of better terms.   Not sure metal gone will do anything?         In my experience you might need to use muriatic acid to get the PH/Alk down in most cases ph down will work but in yours may not.    Hopefully chemgeek will chime in!!

[mandtra]

Just so i understand , your talking about dropping the TA to a ** 0 **       what is the lowest you would drop the ph   ?

[kurt6137]

 I am not as well versed and technical as chemgeek, but I have owned three hot tubs in my day. All I can tell you, is the best way to get rid of scale, which if it is heavy, is  to drain tub and clean filters, use vinegar and water solution with soft cloth or hot tub pad (used specifically for cleaning a hot tub surface) What I have found with PH and Alkalinity, is to adjust it very slowly, wait at least 24 hours before taking measurements, before adding and increasers or decreases. I have screwed this up myself, with testing every 3 hours, when i had my first tub, then adding the increasers and decreases too soon, totally screwed up my tub, with that approach, I ended up with heavy scale, (the filter had heavy scaling too.)  which is why i drained it and started from scratch. I learned my lesson, I add very conservatively and also test my water at the dealer periodically, which means not entirely relying on test strips. Just my opinion.

[chem geek]

If the water was hot at 104ºF then when the pH was 8.1 then with your other water parameters the calcite saturation index was +0.6 so it's not surprising you got calcium carbonate scale.  In a spa, anything above around +0.3 has a risk of scaling and in an acrylic spa there is no need for even a 0 saturation index.  Your Total Alkalinity (TA) is too high and contributes to the outgassing of carbon dioxide which makes the pH rise, especially when your jets are aerating the water.

The suggestion of lowering the pH and TA significantly is a good one as it will help to dissolve the scale (and then dump that water after the scale is dissolved).  You don't want the pH to be very low for too long since you want to avoid metal corrosion, but you could get down into the 6's in pH to dissolve the scale and be OK (it would take 7 fluid ounces of full-strength Muriatic Acid in 350 gallons or 9.4 ounces weight which is about 6.3 ounces volume of dry acid to get down to a pH of 6).  If the TA were brought down to 0, then that's roughly a pH of 4.5 which is lower than you'd want -- for a short time it might be OK but I wouldn't risk it.

After you deal with the scale, you will want to keep your TA lower and I'd have your CH at no more than 120 ppm to be safe.  If you need additional pH buffering, then you can use 50 ppm borates (from boric acid).

[mandtra]

"and in an acrylic spa there is no need for even a 0 saturation index"     Whats that mean ?  I know about the index , but how does that apply to an acrylic tub ?

Ok , i will keep the CH 120 maximum      PH 7.4-7.5 ?   and TA  70-80  ?

and on a last note ,  how do you feel about some of the other products the pool stores recommend adding to your hot tub ?  such as   Enzyme ? , PH buffer ? , phosphate remover ?, metal out weekly ?

[chem geek]

A 0 saturation index means that the water is saturated with calcium carbonate which you do by having calcium hardness (CH) and total alkalinity (TA) which represents carbonates in the water.  This is needed to protect dissolving of plaster surfaces and grout between tile, but is not needed in an acrylic spa.  So you can have the TA and CH be lower as needed and not have problems.

A properly managed spa does not need extra products -- no enzymes, algaecide, phosphate remover, metal out, clarifiers, flocculants, etc.  Well, I suppose if your fill water is high in metal content then you would need to deal with that, but the other products are not generally needed.

How are you disinfecting your tub?  Are you using chlorine or bromine or something else?  What products are you using and what do you want to use?  There are several different methods each with different pros and cons.

[mandtra]

I'm using the Bromine  floating frog system , and using dichlor as a shock . I really don't want to use anything that i don't have to .  I would like it to be as low of maintenance as possible

I have been using metal out & enzyme , .

Being that it  is an acrylic tub and i can run lower amounts of CH & TA.   What are the numbers you would recommend i maintain when i refill ?

This is what my tap water test ***    PH 8.5   TA 20     CH 20        Taylor R-2006

P.S.  I just checked and after adding the acid and the ph is somewhere around a 6.0  or so  the scale is starting to dissolve  almost all gone

[chem geek]

The Dichlor should be somewhat net acidic so should help with the pH, but I think you need to keep your TA at around 50 ppm and I suggest you also use 50 ppm borates (from boric acid) since that will slow down the rate of pH rise.  You can get boric acid from AAA Chemicals or from The Chemistry Store.  You can use The Pool Calculator to calculate dosing.

[mandtra]

well the suggestions worked very well. the scale is completely gone ,   So i dumped the tub cleaned and have refilled.

[mandtra]

I'm trying to follow the recommendations  , but want to make sure i have this right.

PH  7.4-7.5
TA  50 
CH  120
Boric acid 50ppm

those settings wont damage my tub?   what about the index ?

[mandtra]

also the ph is been more stable this time so far.      What about the ph buffer ?   good or bad ?

[chem geek]

Those settings will not damage your tub.  Just note that there is more carbon dioxide outgassing at lower pH so don't try and fight to keep the pH low.  If it tends to settle at 7.7 or 7.8, then leave it there.  Of course if it creeps up to 8.0 or more, you can lower it back down but don't lower it to 7.2 since that will just have it come back up more quickly.  I'm glad the pH is more stable now.

By the "pH buffer", are you referring to the borates (boric acid)?  They are fine and the TA of 50 ppm is fine as well since you've got the additional pH buffering from the borates.

[mandtra]

i was talking about the ph buffer they sell in bottles ?     i have the boric acid on order ,but it  hasn't arrived yet