Testing fill water

[Desiato]

My TA has been slowly creeping up and after putting two and two together realised it was caused by my fill water. I keep my TA at 70 and PH at 7.4 because my CH is off the scale at 640 (and rising) and this morning decided to test the TA out of the garden tap, it was 250.

I tested the kitchen sink tap water and it was 180, hmmm quite a difference. I decided to fill the pool for 2 minutes to get the standing water out of the pipes and tested again, this time 160. So I've found out why my TA is always on the up (PH stays firm at 7.4) and I've also found out not to test the fill water without running it for a few minutes.

Anyone else discovered this about higher TA from standing water in the pipes and is 160/180 good/bad/average for tap/fill water?

Thanks

 

[Desiato]

I've just had a thought. In the beginning I was weighing up which way to go with my PH and TA and with the advice of another poster here, I went with a slightly higher PH and a slightly lower TA as that would give me a bit of wiggle room with the PH but having given it a bit more thought, I think I might be better off the other way round.

The guidelines for PH are 7.2 to 7.8 so to have a target PH of 7.2 means I don’t have much wiggle room should it slip out of the safe zone. My PH is pretty stable though and nothing seems to make it rise (no spa or waterfall) and nothing seems to make it fall (apart from when I add acid). So on that basis, here’s my thinking…

My TA will always be creeping up so I will always be adding acid to get it down. Remembering how the PH level effects the rate at which TA falls (the lower the PH the more the TA will fall), it makes sense to me keep the PH at 7.2 and balance this with the TA slightly higher at 90 (instead of 70).

A few other things to consider.

My aeration method is slow, I have some 3/4” PVC elbows attached to the returns which causes the water to break the surface but it can take 24 hours to raise the PH 0.1 (with the pump running 24 hours). I need to see how I can create more bubbles.

My electricity is expensive and I am now only running the pump for 4 hours over night.

I’m seeing a few small orange stains near the bottom drain. I don’t think they have always been there but I can’t be sure as I haven’t seen the deep end drain so clearly before. Would a TA of 70 or 90 be better at stopping stains forming?

My current numbers are:

PH - 7.4
TA - 80
CYA - 55
CH - 640
FC - 6.0
CC - <0.5
CSI 0.02
Water temp 84F

With my TA at 70 and my PH at 7.4 I get a CSI of 0.02. If I change my PH to 7.3 and my TA to 85 I maintain a CSI of 0.02, This sounds like a better compromise to me. 7.2 PH would need a TA of 100 to give me a CSI 0.01 so that is also an option.

Thoughts, recommendations?

 

[Desiato]

Guess I'll stick with my own conclusion of 7.3pH and 85 TA and see how that works.

 

[oldguy70]

Guess I'll stick with my own conclusion of 7.3pH and 85 TA and see how that works.

Hi, I see no one has responded, I am no expert by any definition, but my guess is any CSI that ranges from -.15 to +.15 has a margin of error and if you are within the guidelines of PoolMath numbers you would be safe. I figure that the pool is constantly adjusting throughout the day so maybe in the AM you are in the - range and throughout the day your pool heads for the + range, then you add your chlorine, acid or whatever and the cycle starts again.

I try to keep my plaster pool within those CSI numbers and play with my TA & pH the best way I can, so if one day my pH is a bit high or TA a bit low I can easily adjust....you fight TA that is rising, I fight TA that goes down because I use a lot of acid to balance the pH.

 

[smackdab]

My fill waters TA is 270 ppm so you're in better shape than me. If it doesn't rain for awhile and I have to add fill water alot then I have to start hitting the muriatic acid to get my TA back down. A lower TA will lower the CSI but that is mainly for calcium scaling. You described an orange stain and I don't think that is calcium. Try rubbing a trichlor tab and then a vitamin C tablet on the stain and see if it disappears.

 

[Desiato]

I suspect the orange stains are iron and have some vitamin C standing by but I don't have any sequestrant yet so I'll hold off on that for now. My concern about the stains was that they may be being caused because my TA is on the low side. I've read a number of websites that say you want to keep your TA between 80 to 120 but I've taken them with a pinch of salt as I've also read that CC of 3.0 is also perfectly fine.....yeah right!

I think through the process of writing the post I've kind of worked out what I need to do. I can lower TA fairly easily with acid but I struggle to raise PH as my aeration method isn't great so that's one area I need to work on. I remember seeing one of chem geeks graphs that showed you need less acid to lower TA and PH when the PH is lower to start with. This is why the optimal way to lower TA is to add enough to take your PH down to 7.0, raise your PH to 7.2 and then add more acid to take it back down to 7.0 and repeat until you reach your desired TA level. If I go with a slightly lower Ph of 7.3 from my current 7.4, that means my TA can be 85 which moves it out of the danger zone (if 70 really is a danger zone?) and means I can let my TA creep up a little bit without worrying about it. It also means I use less acid to lower the TA as the PH is starting from a slightly lower point.

I think one of the reasons I didn't get any original responses is because I'm probably fussing over nothing. It says on the site not to worry too much about TA and not get too fixated with adjusting levels just to reach a target (like 0.0 on the CSI scale) but I couldn't help myself. The pool is sparklingly clear so I needed to find something to fiddle with.

Thanks for your input guys.

 

[smackdab]

You need more acid to lower 7.2 to 7.0 than lowering from 7.4 to 7.2 so that would make lowering your TA level a little faster. You can go down to a minimum TA of 60. Just keep lowering your TA until your pH holds steady. Here is another Chem Geek chart that shows the CO2 outgassing at different TA and pH. My pH holds steady at 70-80 ppm TA and I havent added acid in a month because I haven't had to add much fill water in that time. I feel its worth lowering the TA to the right amount instead of fighting pH rise so much.

 

[Desiato]

You need more acid to lower 7.2 to 7.0 than lowering from 7.4 to 7.2

Are you sure, I thought it was the other way around?

 

[Texas Splash]

That's correct - acid. Please see this page for a thorough explination: Pool School - Lower Total Alkalinity.

 

[smackdab]

Are you sure, I thought it was the other way around?

I'm sure.

Open Pool Math and for the PH type in 7.2 and 7.0, then type in 7.4 and 7.2 and see the difference in acid amounts. Also try 8.0 and 7.8.

 

[chem geek]

Because of your high TA fill water you will be adding acid regularly to keep the TA and pH from climbing, but maintaining a lower pH and keeping a higher TA level will result in more carbon dioxide outgassing that will require more acid. There is an outgassing rate that will require an amount of acid that will balance the TA lowering from acid with the TA rise from evaporation and refill, but it is unlikely that this balance point is at low pH and high TA.

Basically what you should do is add acid to keep the pH at a certain level and notice what happens with the TA over time. If the TA drops, then that means your pH target is probably too low while if your TA rises then that means your pH target is probably too high.

Let's work this out at least approximately. You have a 15,500 gallon pool and let's assume it's an average of 4.5 feet deep (3 foot shallow end, 6 foot deep end) and let's assume 1/4" (about 6 mm) per day evaporation. With no water dilution and just accounting for evaporation and refill and assuming 170 ppm TA this would be a TA increase of 24 ppm per month. The amount of acid needed in 15,500 gallons to compensate for this rise is 95 fluid ounces (2.8 liters) of full-strength Muriatic Acid (31.45% Hydrochloric Acid) per month. If this was the correct calculation for your TA gain, then this amount of acid (added in smaller amounts over the month, of course) would result in a constant TA level and would settle in at a pH where the outgassing rate matched the acid amount in terms of keeping pH stable. If this pH is in a reasonable range, then if your saturation index were too far from zero then you could compensate by adjusting the CH level.

 

[Desiato]

I'm sure.

Open Pool Math and for the PH type in 7.2 and 7.0, then type in 7.4 and 7.2 and see the difference in acid amounts. Also try 8.0 and 7.8.

I did that shortly after I posted the question (changed 7.4 and 7.2 to 7.2 and 7.0) and saw that the amount of acid required increased. I remember when I first read about the method to lower TA and seeing chem geeks chart it sunk in that carbon dioxide outgassing happened quicker at lower PH levels but my brain made the leap that this required less acid. My logic being that if there was less outgassing at higher PH levels then you would need more acid to achieve the same level of carbon dioxide outgassing. I've no idea why my brain did that, I shall have to take it aside and have a quiet word with it.

Cheers for clearing that up.

 

[Desiato]

Basically what you should do is add acid to keep the pH at a certain level and notice what happens with the TA over time. If the TA drops, then that means your pH target is probably too low while if your TA rises then that means your pH target is probably too high.

In my 2nd post I said that my PH is very stable at 7.4 and that the TA rises slowly due to the TA level of the fill water. I guess what I need to find is a happy medium between cost and effect. A PH level of 7.4 will save me a few pennies in acid (thanks smackdab) but that requires a TA level of 70 (to maintain my CSI of 0.02) which may or may not be contributing to the few little orange stains I'm seeing. If lowering my PH to 7.3 and raising the TA to 85 resolves this problem then that is a cost I'm willing to bear.

All of these little tweaks keeps my CSI in the 0.02 to 0.04 range with my current temperature of 82F. My CH is a problem at 640 and I can't afford to drain it so unless there is some other simple way of lowering it (no, I didn't think so), then these are the figures I have to work with. Maybe I'm being a little too fixated on trying to keep my CSI as close to 0.0 as possible? I haven't suffered from scaling even prior to starting the TFP method so maybe raising my PH to 7.5 and my TA to 80 (which gives me a CSI of 0.17) is the better way to go? (less acid due to the slightly higher PH and keep a record of how long it takes the TA to rise to 90).

 

[pooldv]

Yes, there is no reason to target csi to that narrow of a range. Anything from -.6 to +.6 is fine. Or if you want to be extra careful keep it in the recommended range for new plaster which is -.5 to +.5. I would leave PH alone if it is happy at 7.4 and let TA be what it is. And definitely don't raise TA to try to get to a different csi number that is still well within the recommended range.

 

[chem geek]

In my 2nd post I said that my PH is very stable at 7.4 and that the TA rises slowly due to the TA level of the fill water. I guess what I need to find is a happy medium between cost and effect. A PH level of 7.4 will save me a few pennies in acid (thanks smackdab) but that requires a TA level of 70 (to maintain my CSI of 0.02) which may or may not be contributing to the few little orange stains I'm seeing. If lowering my PH to 7.3 and raising the TA to 85 resolves this problem then that is a cost I'm willing to bear.

So with the TA rising slowly that means you aren't adding quite enough acid so if you added more then your equilibrium pH would be a tad lower, perhaps 7.3 OR you could let the TA rise and then the pH will rise more so you'll add more acid. That sounds like the equilibrium point for acid addition with stable TA and pH given your evaporation and refill. Of course, this will all change as weather changes but at least you won't try and fight battles you won't win via chemical parameter settings. You could, of course, use a pool cover that would eliminate evaporation. That will also help keep the CH from rising as well.

As for scaling, we don't usually see that until rather high CSI around +0.7 or higher. It's in SWG cells where scaling occurs even with bulk water 0 CSI which is why one normally targets slightly negative CSI and uses borates in such SWG pools. So yes, you can let your TA rise some and you'll have the pH rise and need to add more acid but you'll then be at the balance point where both should be stable. You're pretty close to that already. So no need to change anything due to CSI, but you can let the TA rise some to get to the stable pH AND TA point (again, subject to change as weather changes).