Heater damage from low TA?

[Kidney]

I have a Hayward H400FD running on natural gas in line with my pebble sheen pool (refinished more than a year ago). It has a cupro-nickel heat exchanger. Hayward recommends a min TA of 80. I use bleach to sanitize. Would it be safe to this heater to set the TA to 70 to counter fairly frequent pH rises?

Also, I see that if I raise the CH from my current 180 ppm to the max recommended of 400 ppm, then my saturation index would be closer to 0. Is it ok to do this?

Once I have all these balanced, I am thinking of borating the pool.

Thanks,
Kidney

 

[TomBorg]

Welcome to the forum!

Low pH can corrode the copper pipes in the heater, damaging them, and leading to copper in your pool water, which can cause stains and green hair.

I assume Hayward is recommending the TA of 80 to prevent dramatic changes in pH that can lead to the afore-mentioned corrosion. A low TA by itself shouldn't directly cause problems in the heater. (I'll mention the name "chem geek". Hopefully he'll chime in to correct me if I'm wrong.)

As long as you are not using an acidic form of chlorine (e.g. tablets), and you check your pH every day or two, using a TA of 60-70 should be fine.

 

[jblizzle]

Welcome to TFP!!!

I agree with Tom, a low pH is WAY more of a problem to the heater than the TA a little lower than their recommendations.

 

[chem geek]

Yes, it is OK to raise your CH when using a lower TA so that you have a balanced saturation index to protect your Pebble Sheen pool surface. You do not need the TA nor CH in order to protect the heater. To prevent metal corrosion it is most important that your pH not get too low for too long. So you can target a higher pH (say 7.7 or 7.8) and that will not only have somewhat lower corrosion but helps to balance the saturation index and the rate of pH rise is slower at higher pH as well.

Many pool recommendations in the industry are based on having pools that use Trichlor which is acidic so they want to make sure you have sufficient TA at all times to prevent a pH crash. They mostly don't want the pH to get too low. In your case, cupro-nickel is far more resistant to corrosion than copper alone, though even copper alone is not a problem especially in your pool that doesn't have a saltwater chlorine generator (does it? you didn't mention it) so doesn't have the elevated corrosion rate from a higher salt level.

 

[Kidney]

Good and thank you!

It looks like Hayward is just giving industry-accepted ranges so I'm not sure the min of 80 is even that important. My problem is that pH tends to rise so no risk of a low pH corroding the heater. I understand that once I borate the pool it'll be hard to change the TA hence my double checking 70 is ok. Hopefully chemgeek sees no issue with a TA of 70 for this cupro-nickel heat exchanger either (assuming pH is kept between 7.4 and 8.0 max).

I am using Trichlor pucks just this week to increase CA back to 50 (went down to less than 20 after huge Texas rains last month). The pool's calcium hardness also dropped from 260 to 180 but it looks like the SI could be made to reach 0 if CH is increased to 400, I just don't know if that's something sensible to do (since it's hard to lower CH once it's up).

 

[chem geek]

You're fine to lower your TA and to raise your CH. If you had an SWCG then you'd target a slightly negative CSI (around -0.2) to reduce the amount of scaling in the salt cell (the borates significantly help with that as well).

 

[Kidney]

Thank you chem geek. It looks like I was replying to TomBord and Jason when you replied to me...

I do not have a SWCG. I am using grocery store bleach (and Trichlor only once or maybe twice a year for a few days when my CA needs to go back up as right now). Looking at the Hayward heater documentation, they do recommend chlorine between 1 and 3 ppm, pH between 7.4 and 7.6, TA between 80 and 120 ppm, CH between 200 and 400 ppm. Up to so far, I have tried to keep pH in this range but it consistently rises to 7.8 or sometimes 8.0. That's one reason I am interested in borating the pool (to reduce the number of times I need to add MA). So if I understand correctly, as long as my CSI is as close to 0 as possible, I only need to focus on making sure the pH is not too low. Hayward says a pH higher than 7.6 can result in scaling of the heat exchanger: not sure how much of a concern that is if I target a pH of 7.7 or 7.8.

I am trying to get everything balanced before I can borate (and I shall start another thread with questions I have on this process). I am coming out of one month of very heavy rain here in TX after a 10-day period without a pump. Simply using BBB and a reasonable amount of daily brushing I was able to avoid the pool turning green during these 10 days while my Hayward 3400 VSP was being serviced (it was less than a year old and the motor just stopped working, not impressive at all but at least Hayward honored their 3-year warranty when they changed both the motor and the drive, which I learned has to be changed every time the motor is changed).

 

[chem geek]

Hayward is absolutely wrong to only mention ONE parameter (pH) as if that is the only source of scaling. If you had less than 50 ppm CH in the water (with TA 80 ppm) then even if the pH were 8.5 you wouldn't get scaling. So forget what Hayward is telling you in their manual since it's very clear that they have oversimplified their advice to the point of being completely useless. They also clearly do not understand the chlorine/CYA relationship since their 1-3 ppm FC with no CYA would be a HUGE amount of active chlorine that is at least 16 times higher than what is present with the FC/CYA levels we recommend (so 4 ppm FC with 50 ppm CYA or 5 ppm FC with 80 ppm CYA).

If you manage your CSI so it is near 0, you won't get scaling in their heater. Note that their heater when on will be around 30ºF hotter at the surface of their heat exchanger so will be around +0.2 CSI units higher, but that isn't enough to have significant scaling. You don't have to have your CSI right at 0 -- just be reasonably close to it. So you can certainly have your pH settle in near 7.8 without a problem if your TA, CH and water temperature are such that your CSI isn't too high (for scaling) or too low (for dissolving of plaster).

So if you plan to target a higher pH of 7.7 or 7.8, then you wouldn't get your CH up to 400 because even with your TA down at 70 ppm and I presume a CYA of around 50 ppm you'd only need a CH of around 250-300 ppm to have a near zero CSI. Put in the numbers into PoolMath including your usual pool temperature.

Also, are you sure your pH rise is due to carbon dioxide outgassing that a lower TA and higher pH would address? If your pH rise is from carbon dioxide outgassing, then you would likely see your TA drop over time as you've added acid over time. Is that what you are seeing? If not and if instead you find your CH to be rising over time, then you may still have some plaster curing or calcium hydroxide release from it and a lower TA or higher pH target isn't going to help with that.

 

[Kidney]

chem geek, the week has been busy... Thank you for your explanations that did clarify all I need to do to avoid heater (and pool finish) damage is to check my CSI fairly regularly and ensure it does not drift beyond acceptable values. Easy enough! Re Hayward's documentation, it does not discuss Cyanuric Acid at all, which is indeed surprising but I keep mine at 50.

My TA does not drop, it remains constant at 80. My pH rises fairly quickly (in 3 or 4 days) from 7.4 to about 7.8 and possibly 8.0 or higher (after 2 weeks or so) if I do not lower it. To lower pH back to 7.4 on almost a weekly basis, I find myself having to add baking soda to first raise TA a notch before adding MA, which lowers both TA back to 80 and pH down to 7.4. I find the frequency of having to do this (weekly sometimes a bit longer) cumbersome, hence in part why I am interested in adding borates. I would be curious to know what would happen to my pH if i did not lower it as described: I don't know where it would settle but I hesitate to let it rise too much as I believe this would wreak my CSI havoc and do some damage to heater, other parts, or to the Pebble Sheen finish.

I have another question. I will soon have to leave the pool unattended (but filtered, i.e. the pump will operate and the water level be replenished as needed) for five days. Can I simply add 5 times the amount of bleach I would add before a normal sunny day and let the resulting chlorine level deplete over the 5 days so that when I come back the pool has enough chlorine left to be at or above the recommended value?

 

[chem geek]

If you are adding baking soda then that means your TA is dropping over time IF you didn't add the baking soda. That's what I meant. So having your TA lower should help some. The borates may not reduce the total amount of acid you add, but it will reduce the rate of pH rise and hence the required frequency of acid addition. I would also suggest that you not lower your pH as much. When you use the borates, you may be able to just lower it from 7.8 to 7.6 and that will also help reduce the amount of acid you add because lower pH outgases more carbon dioxide faster.

As for chlorine depletion, it loses a percentage each day so if you know what that drop is then you can predict what will happen over 5 days. The easiest thing to do is to just use a Trichlor puck. It won't increase CYA by very much over just 5 days. At 2 ppm FC per day, it would increase CYA by only 6 ppm.

 

[Kidney]

If you are adding baking soda then that means your TA is dropping over time IF you didn't add the baking soda. That's what I meant. So having your TA lower should help some.

Do you mean that I should reach a point (if I first lower the TA to 70 and reduce pH from 7.8 or higher to 7.6 instead of 7.4) where I would no longer observe TA dropping? That would be really nice as adding baking soda every time I need to drop pH is not only annoying but wasteful.

As for chlorine depletion, it loses a percentage each day so if you know what that drop is then you can predict what will happen over 5 days. The easiest thing to do is to just use a Trichlor puck. It won't increase CYA by very much over just 5 days. At 2 ppm FC per day, it would increase CYA by only 6 ppm.

Ok, so either a Trichlor puck or 5x my usual bleach addition and the pool should be fine. Am I understanding correctly that in my 14K gallons one Trichlor puck adds 6ppm CYA? In other words to raise it from 30 to 50 ppm I would need to add a little more than 3 pucks? I get my 3" Trichlor pucks from Leslie's. They are 99% active ingredient.

 

[chem geek]

As your TA gets lower and you use a higher pH target that should result in slower carbon dioxide outgassing, a slower pH rise, and use of less acid so a slower TA drop (since the TA drop only comes from acid or net acidic chemicals).

I should have wrote Trichlor pucks, plural. You can use PoolMath to see that 10 ppm FC (5 days at 2 ppm FC per day) would need 20 ounces weight of Trichlor which is 2-1/2 pucks at 8-ounces each. That number of pucks would raise the CYA by 6 ppm.

To raise the CYA from 30 to 50 ppm, so a 20 ppm increase, you need to add 20/0.61 = 32.8 ppm FC of chlorine from Trichlor so that would be 67 ounces of Trichlor so 67/8 = 8.4 pucks.