New Fill: Weird Taylor Test Kit Ph Reading W/acid Demand Drops

[pdampier]

I drained and filled the tub this last weekend...

With fresh water the readings were:

CH: 30

TA: 10

ph: >8

So I first got the CH up to 150. Then adjusted TA to 80-90 (5oz baking soda) and retook the pH and it was stil >8 (expected).

In order to work out how much dry acid to add I added a drop of the acid demand reagent to the Taylor pH test. However it IMMEDIATELY went to a <7 pH color. Why would this be?

Using test strips the reading appeared to be around 7.8 to 8 so I added 0.5oz of dry acid at a time over the course of a day (2 oz added so far) and now Taylor reads around 7.4 to 7.6...

Any reason for this weirdness?

[chem geek]

What you saw would make sense if you added the acid demand drops BEFORE you added the baking soda to adjust TA. However, I don't know why it moved so much afterwards unless the baking soda didn't increase the TA as much as you thought (perhaps it wasn't mixed into the bulk water yet?). It is true that one drop in the acid demand test does move the pH more than one would like at a TA of 80 or so, but it's still only around 0.2 to 0.4 units -- not more than 1 unit. That's strange. I wonder if the acid demand drops are too strong for some reason. By the way, after adding 2 ounces (weight?) of dry acid, the TA may be down to 65 ppm now.

[pdampier]

What you saw would make sense if you added the acid demand drops BEFORE you added the baking soda to adjust TA. However, I don't know why it moved so much afterwards unless the baking soda didn't increase the TA as much as you thought (perhaps it wasn't mixed into the bulk water yet?). It is true that one drop in the acid demand test does move the pH more than one would like at a TA of 80 or so, but it's still only around 0.2 to 0.4 units -- not more than 1 unit. That's strange. I wonder if the acid demand drops are too strong for some reason. By the way, after adding 2 ounces (weight?) of dry acid, the TA may be down to 65 ppm now.

Ah that could be have been it - maybe I took the initial pH earlier than I remember and it was before the TA was increased to 80-90.

Yes the 2oz of dry acid was weight based and I found the pH was again high (~8) this morning so I added another 0.5oz of dry acid (mixed in a pail before adding). I tried acid demand test again and with one drop it "only" changed from 8 to 7.4 so perhaps things are stabilizing now?

Historically I've found this water seems to stabilize with a lower TA - I tend to start around 80-100 but then find things working better with the TA at 40-50 or so. Is that a problem or a concern - Its an arcylic based spa?

Thanks so much for the help!

[chem geek]

So long as you aren't using regular acidic sources of chemicals (including Dichlor, Trichlor, MPS non-chlorine shock) where the pH tends to drop over time, then having the low TA is not a problem. I think 50 ppm is a good low-end and that assumes that Cyanuric Acid (CYA) isn't higher than 30 ppm (CYA contributes to TA). With acrylic you should be fine. If you wanted more calcium carbonate saturation, you could always increase Calcium Hardness (CH), but I don't think that's necessary and your 150 ppm is decent, especially if your pH tends towards 7.7-7.8 or so.

[pdampier]

So long as you aren't using regular acidic sources of chemicals (including Dichlor, Trichlor, MPS non-chlorine shock) where the pH tends to drop over time, then having the low TA is not a problem. I think 50 ppm is a good low-end and that assumes that Cyanuric Acid (CYA) isn't higher than 30 ppm (CYA contributes to TA). With acrylic you should be fine. If you wanted more calcium carbonate saturation, you could always increase Calcium Hardness (CH), but I don't think that's necessary and your 150 ppm is decent, especially if your pH tends towards 7.7-7.8 or so.

Thanks - I don't use chlorine so CYA isn't a concern but I do use Bromine and MPS - Is that an issue? On the last fill I found I pH would slow drop and maybe every 1 or 2 weeks I'd add soda ash to move from say 7.2 to 7.6 and then wait while it dropped over another few weeks.

[chem geek]

Thanks - I don't use chlorine so CYA isn't a concern but I do use Bromine and MPS - Is that an issue? On the last fill I found I pH would slow drop and maybe every 1 or 2 weeks I'd add soda ash to move from say 7.2 to 7.6 and then wait while it dropped over another few weeks.

If the pH is slowly dropping, then you can raise the TA level a little to see if that helps keep it more stable (the higher TA will tend to raise the pH, thus counteracting the drop you are currently seeing). There should be some TA level where the pH stays reasonably stable over time, though obviously there will be swings after chemical additions.

[pdampier]

Thanks - I don't use chlorine so CYA isn't a concern but I do use Bromine and MPS - Is that an issue? On the last fill I found I pH would slow drop and maybe every 1 or 2 weeks I'd add soda ash to move from say 7.2 to 7.6 and then wait while it dropped over another few weeks.

If the pH is slowly dropping, then you can raise the TA level a little to see if that helps keep it more stable (the higher TA will tend to raise the pH, thus counteracting the drop you are currently seeing). There should be some TA level where the pH stays reasonably stable over time, though obviously there will be swings after chemical additions.

I will give that a try. Right now though pH still seems to be drifting upwards each day. Yesterday AM I added 0.5oz of dry acid and it reduced the pH from ~8 down to 7.6 and that was holding when I checked it in the evening. However this morning it was back up to >8.0. I added another 0.5oz of dry acid (now 3oz since the fill) and I will test again tonight but seems like I'm still at a point of pH drifting upwards. The hot tub is not being used so no airation/jets etc raising pH....

[chem geek]

Mmmmm. That's strange. There is still outgassing even with no aeration, but isn't very fast unless the TA is high and yours isn't very high. You can see what happens as the TA gets lower from continued use of acid. If the rate of pH rise slows down, then it's the TA level; otherwise the source of pH rise is something else and I don't know what it is.

[pdampier]

Mmmmm. That's strange. There is still outgassing even with no aeration, but isn't very fast unless the TA is high and yours isn't very high. You can see what happens as the TA gets lower from continued use of acid. If the rate of pH rise slows down, then it's the TA level; otherwise the source of pH rise is something else and I don't know what it is.

Yeah its really weird given this is a fresh fill and levels were pretty stable before.

Last night I got home and found pH was still ok (~7.6) but again this morning it was up over 8.0. So I added another 0.5oz of dry acid.... I think that now makes a total of 3.5oz's. I will re-test pH and TA tonight to see where the TA is now. If I started around 80-90 (raised from 10 out of the tap) I'd imagine I'm down to 50 or less by now...

Not sure why the pH keeps rising so fast though....

[pdampier]

Tested tonight and the 0.5oz dry acid this morning lowered pH to 7.6.... Tested TA (since about 3.5oz of dry acid now added) and its down from 80-90 to 60.

I'll test pH tomorrow AM and see if it is back up to 8 or more.....

[pdampier]

This morning it was back up to 7.9 or so (not quite 8) - Added another 0.5oz of dry acid!

[chem geek]

Without aeration, I wonder what the heck is contributing so much to your pH rise. So far, it doesn't seem to be slowing down much at lower TA, though we'll see what happens after this latest acid addition. By any chance, you don't happen to have an ozonator, do you?

[pdampier]

Without aeration, I wonder what the heck is contributing so much to your pH rise. So far, it doesn't seem to be slowing down much at lower TA, though we'll see what happens after this latest acid addition. By any chance, you don't happen to have an ozonator, do you?

Yes I do have an ozonator and a 24/7 circ pump so I see bubbles out of the ozonator "jet" 24/7 so that would contribute some... However, on the last fill I would normally need to add Soda Ash to raise the pH about every 2 weeks so the ozonator didn't seem to be raising pH much last time around since it would drop over time... (I use Bromine and MPS but the tub has very low use so I only add a small amount of MPS every 2-3 weeks or so)

I tested again last night and it had gone from 7.9 down to 7.6 with the 0.5oz of dry acid.

This morning though it was back up again to 7.8 - So the rate of climb does seem to be slowing.

I hedged my bets and only added 0.3oz of dry acid this morning....

I will test again this evening and check TA again as well....

[pdampier]

Well on Friday evening pH was 7.6....

Saturday AM it was 7.8 so I added another 0.3oz's of dry acid.

Saturday PM it was 7.4

Sunday AM it was 7.6

Feels like things maybe stabilizing but I bet its at 7.8 or more on Monday AM!

[pdampier]

Even stranger - Still have the problem.

Tonight pH was back up to 8.0 and TA is now only 40.

I added yet another 0.3oz of dry acid.

No idea what is going on here.

[chem geek]

I've got no idea either, especially since this didn't happen before (i.e. before this fill) and nothing seems to have changed.

[pdampier]

I've got no idea either, especially since this didn't happen before (i.e. before this fill) and nothing seems to have changed.

If the TA gets down to 20 or 30 and things stabilize is that a problem? It feels like the pH rise each day is slowing....

[chem geek]

Well, if the TA is that low then there isn't very much pH buffering. If you added 50 ppm Borates, then you'd have more buffering, though that's a better buffer (at spa pH) against a rise in pH and not as much capacity against a drop -- of course, that doesn't seem to be a problem in your situation since the pH tends to rise so perhaps it will be OK, but I don't like the idea of having the TA that low below 50 ppm.

Is your CYA level 30 ppm? At a TA of 40 ppm with that CYA level, then at a pH of 8.0 the outgassing of carbon dioxide would stop completely. So if there were any pH rise beyond that then it has to be from some other source. If there were a way of turning off your ozonator (the air injection as well), then that would eliminate that possibility.

Is the spa covered most of the time?

I'd try the borates before getting any more extreme with the TA.

[pdampier]

Well, if the TA is that low then there isn't very much pH buffering. If you added 50 ppm Borates, then you'd have more buffering, though that's a better buffer (at spa pH) against a rise in pH and not as much capacity against a drop -- of course, that doesn't seem to be a problem in your situation since the pH tends to rise so perhaps it will be OK, but I don't like the idea of having the TA that low below 50 ppm.

Is your CYA level 30 ppm? At a TA of 40 ppm with that CYA level, then at a pH of 8.0 the outgassing of carbon dioxide would stop completely. So if there were any pH rise beyond that then it has to be from some other source. If there were a way of turning off your ozonator (the air injection as well), then that would eliminate that possibility.

Is the spa covered most of the time?

I'd try the borates before getting any more extreme with the TA.

Thanks for all the help with this!

I've never tested for CYA since I use Bromine? Should I?

I'll try adding borates - Is that the 20 Mule Borax laundry booster? If so how much would I add for a 450 gallon spa?

Thanks again... I didn't get a chance to test pH this morning but will check again tonight.

[chem geek]

I've never tested for CYA since I use Bromine? Should I?

I'll try adding borates - Is that the 20 Mule Borax laundry booster? If so how much would I add for a 450 gallon spa?

It would help if I reread posts to refresh my memory! You don't need to worry about CYA. You probably don't have any, unless you used Dichlor to shock/reactivate the bromine (usually you use MPS or bleach, but some people shock with Dichlor in which case you'd build up CYA).

Yes, the borates could be added by a combination of 20 Mule Team Borax plus acid (the Borax by itself raises pH), BUT it's much easier just to get Gentle Spa since it's pH balanced (it's mostly boric acid). It's more expensive this way, but it's not a large quantity for a spa.

In your 450 gallon spa, if you use Gentle Spa, then it's around 2 cups 3 ounces to get to 50 ppm. If you use Borax and acid, it's around 3 cups 1 ounce of 20 Mule Team Borax and 1 cup 3 ounces of dry acid (sodium bisulfate). However, I would add portions of each alternately so as not to make the pH swing too high (or you could mix these in a bucket of spa water before adding it back in). You can also use The Pool Calculator to figure dosing.

[pdampier]

I've never tested for CYA since I use Bromine? Should I?

I'll try adding borates - Is that the 20 Mule Borax laundry booster? If so how much would I add for a 450 gallon spa?

It would help if I reread posts to refresh my memory! You don't need to worry about CYA. You probably don't have any, unless you used Dichlor to shock/reactivate the bromine (usually you use MPS or bleach, but some people shock with Dichlor in which case you'd build up CYA).

Yes, the borates could be added by a combination of 20 Mule Team Borax plus acid (the Borax by itself raises pH), BUT it's much easier just to get Gentle Spa since it's pH balanced (it's mostly boric acid). It's more expensive this way, but it's not a large quantity for a spa.

In your 450 gallon spa, if you use Gentle Spa, then it's around 2 cups 3 ounces to get to 50 ppm. If you use Borax and acid, it's around 3 cups 1 ounce of 20 Mule Team Borax and 1 cup 3 ounces of dry acid (sodium bisulfate). However, I would add portions of each alternately so as not to make the pH swing too high (or you could mix these in a bucket of spa water before adding it back in). You can also use The Pool Calculator to figure dosing.

Hmmm not sure I have that much dry acid left now - Need to go order some 'Gentle Spa' I guess!!

Checked tonight and pH is now 7.8 again so on the way back up.... What is also strange is I checked with test strips and these (aqucheck bromine strips) seem to indicate the pH is low 6.8 or so) - The Taylor test kit (new reagent) shows 7.8.... So now I'm not even sure I trust the results I'm seeing!

[chem geek]

Hmmm not sure I have that much dry acid left now - Need to go order some 'Gentle Spa' I guess!!

Checked tonight and pH is now 7.8 again so on the way back up.... What is also strange is I checked with test strips and these (aqucheck bromine strips) seem to indicate the pH is low 6.8 or so) - The Taylor test kit (new reagent) shows 7.8.... So now I'm not even sure I trust the results I'm seeing!

High sanitizer levels, usually above 10 ppm, can bleach out one of the two indicators in the pH dye making it read falsely high, but that would make something like 7.4 look like 8.0 or so -- it wouldn't turn a low 6.8 "yellow" into red. Something is amiss here. I wonder if there is something else interfering. Taylor also says that iron > 10 ppm can cause negative interference, but that's a very high iron level (and I'm not sure which direction is "negative interference"). You might give Taylor a call and ask them what they think.

[pdampier]

I carried on with adding dry acid for a little longer but the same problem existed. TA basically at 10 or less and yet pH would rise over 2 days or so to 8.0 (from 7.4).

So today I added 25oz of the Borax and then used up all the rest of the dry acid (is it sold as a regular product in local stores like Baking Soda is or do I need to order the 93% stuff from a Spa store?) - added the 1 cup 3oz of dry acid and it wasn't enough so added 5.5 oz more and now pH is 7.4 to 7.6 so I'll see if it rises again.

TA also seems to have increased now to 40-50 (test strip mesaurement only)....

[chem geek]

Well clearly your source of rising pH isn't carbon dioxide outgassing, but I have no idea what it is.

[pdampier]

Looks like the borates are helping. Two days in now and if anything the pH has droped very very slightly instead of rising.....

Sitting at 7.4 right now.