Autopilot total control?

[andy]

Couple questions.
1. My total control says ph 7.50 which is good but yet it is ON and pumping acid into the pool.
2. Can my salt be kept lower than 3000? I have an aluminum cover track and the salt is eating it.
3. Do I test everything the same since this is a salt/chlorine pool instead of straight chlorine?
4. On my cemistry controller there is a water sample valve between the orp and ph sensors. When I open the valve to get water....It just lets air into the system. No water comes out.????

Last. In my quest to lower my CC i've shocked the pool with 2 gal of pool shock.(done this twice with no luck lowering CC) and each time when checking the pool a couple days later I have ALOT of fine sandy like grit on the bottom of the pool i've had to vac out. Any idea what this is???

Pool info:
21,000 gal Fiberglass
Indoor with auto cover that is on all the time
Auto Pilot Total Control System(salt/chlorine generator with acid pump)
Sta-rite Mod Media 3 Cartridge Filter
Pool is kept at 84 deg and heated to 88+ sometimes

Test Kit info:
Taylor K-2006C service complete (FAS-DPD chlorine)
Taylor K-1766 sodium chloride (salt water)

Auto Pilot Total Control reads:
ORP 690 high
PH 7.50
salt 3000

Taylor kits read:
FC .6
CC .6
PH 7.3
Alkalinity 120
Calcium Hardness 350
CYA (I couldn't get a reading because the solution never turned cloudy)
Sodium Chloride 3000

I've been adding ProTeam Metal Magic on occasion to help with the brown stains.


Any suggestions are appreciated! Thanks, Andy

 

[JasonLion]

1) The TC system will pump acid at intervals any time the PH reading has been higher then 7.5 recently. The display doesn't show the same level of detail as the reading used to decide to pump acid or not. The display only shows one reading every several seconds, while the actual sensor takes readings more frequently than that. In any case that behavior is normal. It isn't uncommon for the PH reading to show 7.47 and to have acid being pumped. As long as the long term average remains around 7.45 to 7.52 you are fine.

2) Yes, you can run the TC system with salt as low as 2400. However, the closer you get to 2400 the more risk there is of drifting below 2400, which would be bad. Also, I doubt that 2400-2600 would help your track all that much. It is possible to get a sacrificial anode to protect aluminum parts, but I don't know the details.

3) Yes, you test everything the same way and for the same reasons (though FC and PH can be tested much less frequently). The only difference is that you should do a salt test every once in a rather long while to calibrate the sensor in the TC system. Also, don't try to calibrate the PH sensor unless FC is below 2. (Actually calibrating the PH sensor is kind of a pain unless you have a ColorQ, since the sensor in the TC system is so much more precise than the usual Taylor PH test.)

4) To get a water sample from the chemistry controller you often need to close the output valve and then open the sample valve. Otherwise the output tends to draw water more quickly than the input can supply water and the sample valve simply lets air in (though this can vary in some setups). That is only one of several ways in which I find that sample port rather poorly designed. I normally sample water directly from the pool unless I am calibrating the sensors.

 

[chem geek]

See my reply to another thread of yours here. I believe you are seeing corrosion of your aluminum track because of the combination of the salt level and the high disinfecting chlorine level because you do not have Cyanuric Acid (CYA) in your pool.

As for the grit after shocking, it sounds like you were using Cal-Hypo and from your numbers in the other post your pool is over-saturated with calcium carbonate if it is now at a pH of 7.5. Your TA is too high at 120 (from the other post) and this will lead to more scaling on your SWG wearing it out faster. So I suggest you add 20 ppm CYA, set the FC level for your pool to 2 ppm, and lower your TA to 80 ppm, in that order. For shocking, you should use chlorinating liquid or unscented bleach, not Cal-Hypo, because your Calcium Hardness (CH) is already high enough (with Cal-Hypo, for every 1 ppm FC you add, you also get 0.7 ppm CH). On the other hand, you said 2 gallons so that sounds like a liquid source of chlorine and not Cal-Hypo in which case I don't know what the grit is. 2 gallons of 12.5% chlorinating liquid would raise the FC by almost 12 ppm which is quite a lot without any CYA in the water.

The CC of 0.6 ppm is not a serious problem for an indoor pool. I would focus on the more serious issues of corrosion and disinfecting chlorine level (FC and CYA) first.

Richard

 

[Poolsean]

Couple questions.
1. My total control says ph 7.50 which is good but yet it is ON and pumping acid into the pool.
--> Jason's answer is the best way to explain it. I would further recommend that if your test result and the sensor reading's result are different, calibrate the pH reading to match your test.

2. Can my salt be kept lower than 3000? I have an aluminum cover track and the salt is eating it.
--> Being that you have an indoor pool and tend to keep the water temps on the high side, you can afford to go lower with your salt level. However, at 3000 ppm, lowering it to 2500 ppm would not significantly decrease any potential issues with your aluminum cover tracks.
First, is the track prone to frequent wet/dry cycles or is it submerged? The wet/dry cycles may show some effects from the salt. However, if it is wetted or submerged, it is not likely the salt causing the damage.
Second, as Chemgeek mentioned, you have several other contributing factors that would cause the damage to the aluminum tracks:
No Cya. You've reported that the cya test water sample is clear, indicating no cya. Add enough to get to a minimum of 15 ppm (Chemgeek suggests 20 ppm... your choice, it't not a big difference, but enough to produce results in preventing corrosion damage with indoor pools)
High Chlorine residuals. You've mentioned that you are constantly needing to shock the pool to rid the combined chlorine. It is highly unusual for the cc to remain after your repeated shocking. There something else contributing to the consistent cc reading.
Third, electrical bonding may be a possibility. You should have a licensed electrician inspect and verify that the pool is sufficiently bonded. Electrolysis tends to show damage quicker than high salt or high chlorine. Ensure that the Total Control is bonded to the bonding wire loop. Your pump and heater should also be connected to this bonding loop, as should your pool structure. There are many instances with existing pools, that leaks, or damp ground soil conditions, cause the original bonding wire to the pool structure to corrode, leaving the pool unbonded.

3. Do I test everything the same since this is a salt/chlorine pool instead of straight chlorine?
--> Everything tests the same. However, you should see a decrease in having to balance chemicals or maintain cell cleanliness. Ensure that your water test results match with the Taylor Watergram wheel for balanced water. This may also explain why the grit into the pool.

4. On my cemistry controller there is a water sample valve between the orp and ph sensors. When I open the valve to get water....It just lets air into the system. No water comes out.????
--> It's affected by the flow of the water through the flow cell. In most cases, there is sufficient flow of water to allow you to open the center water sample valve and not have the air sucked in. However, in your case, you will have to turn the water return valve (right side) off, prior to opening the center valve to get your water sample. Just make sure you turn the water return valve back on.

Last. In my quest to lower my CC i've shocked the pool with 2 gal of pool shock.(done this twice with no luck lowering CC) and each time when checking the pool a couple days later I have ALOT of fine sandy like grit on the bottom of the pool i've had to vac out. Any idea what this is???
-->I don't know of anything where the process of shocking the pool would cause a gritty fall out. Is it the consistency of sand or is it more flakey? Can you collect some of it and add a few ounces of muriatic acid? Calcium Chloride will react by bubbling and dissolving.

Pool info:
21,000 gal Fiberglass
Indoor with auto cover that is on all the time
Auto Pilot Total Control System(salt/chlorine generator with acid pump)
Sta-rite Mod Media 3 Cartridge Filter
Pool is kept at 84 deg and heated to 88+ sometimes

Test Kit info:
Taylor K-2006C service complete (FAS-DPD chlorine)
Taylor K-1766 sodium chloride (salt water)

Auto Pilot Total Control reads:
ORP 690 high
PH 7.50
salt 3000

Taylor kits read:
FC .6
CC .6
PH 7.3
Alkalinity 120
Calcium Hardness 350
CYA (I couldn't get a reading because the solution never turned cloudy)
Sodium Chloride 3000

I've been adding ProTeam Metal Magic on occasion to help with the brown stains.
--> Proteam Metal Magic contains Diphosphonic Acid, and can be contributing to the cc levels. Have you had any algae growth you've treated for over the past few months? Have you had your water tested for Phosphates? It wouldn't hurt to do a test and treat if needed.
The brown stains are most likely coming from your heater's heat exchanger. 3000 ppm of salt will not cause the heat exchanger to damage...however, high chlorine and low pH levels would.

Any suggestions are appreciated! Thanks, Andy

I'm going to throw this out there as a possibility. IF your phosphate levels are high, over a 100 ppb, the phosphates may be causing an excessive chlorine demand condition that is consuming alot of your chlorine, thus the low chlorine residual. The shocking is enough to allow damage to initiate on the aluminum tracks and the heat exchanger, thus the brown stains.
My opinion is that phosphate is usually the last thing to suspect, when you cannot maintain a chlorine residual. However, it may be the cause for your problems.

Hope this helps,

 

[andy]

Poolsean, Thanks for the reply

I'm going to get the CYA to 20ppm first.

The aluminum cover track is on top of the pool deck(not in the water) and gets water splashed on it everytime someone swims. The water then dries and leaves the salt behind. I am 99.9% sure the salt is what is eating my track. If there is no fix for this, I will have no choice but to remove the AutoPilot Total Control and go to regular water.
Here are a couple pics. This is all the way down the track

 

[JasonLion]

It is difficult for me to be sure what I am seeing. Another shot from a little further away might help to give context.

I see what looks like a metal track set in concrete with white/gray deposits at intervals along the metal-concrete junction. It kind of looks like water is sitting between the rail and the concrete and pushing something out anywhere there are gaps. It is difficult to tell for sure, but that doesn't really look like metal corrosion.

 

[andy]

Those deposits are salt. Once the water dries up, that is what's left. Under the salt is notches eaten out of the track. Here are a couple pics you asked about.

 

[chem geek]

Salt, and specifically chloride, inhibits the formation of the protective passivity layer in stainless steel and I suspect it may also do something similar with aluminum. Aluminum is not particularly resistant to oxidizers so the CYA to 20 ppm should help, but it might not help enough. It's definitely worth a try and would be something you'd want to do regardless of whether you used salt or not. Let us know what happens with this after you've added the CYA.

Richard

 

[andy]

I have 3lb of CYA mixing in a 5 gal pail now. Once I get it disolved, I'll add it to the pool.

Why does my AutoPilot Total Control read 664 ORP today which is close to right on(a bit high) but yet my Taylor test kit reads FC .5 CC .6 which for FC is way low?

 

[andy]

Sorry found the answer in this post.

JasonLion
Mod Squad



Joined: 07 May 2007
Posts: 1997
Location: Silver Spring, MD Posted: Tue Oct 30, 2007 9:18 pm

--------------------------------------------------------------------------------

Welcome to TFP!

To have the ORP reading you have with that low a FC level your CYA level must actually be very close to zero. That is fine and is the traditional recommendation for indoor pools. However it is worth noting that Chem Geek has been recommending using some CYA in indoor pools, contrary to the traditional approach.

 

[chem geek]

Andy,

As you surmised, without CYA in the water the disinfecting chlorine level is quite high so that an FC of .5 registers as an ORP of 664 mV (you earlier said that .6 registered as 690 mV). Every manufacturer of ORP sensor measures differently (which is a whole story I won't get into here), but you will notice that as the CYA gets added, the ORP will go down and your controller will compensate for this by increasing the FC. If your controller tries to increase the FC to something like 8 ppm, then you will want to recalibrate it so that it instead has a target of 2 ppm FC assuming you have 20 ppm CYA. I don't know if your system calibrates based on adjusting the ORP setpoint or whether you can calibrate the FC it reports based on ORP or vice versa or what. Poolsean could probably help out with that.

The bottom line is that your pool should initially target an FC level somewhere in the neighborhood of 10% of the CYA level though we'll probably have you go lower than that in the future by increasing your CYA a bit once we determine whether the CYA is helping with your corrosion problem. An SWG pool can usually have a fairly low FC of closer to 5% of the CYA level, but let's start with the 10% and see how things go -- it's still a LOT less disinfecting chlorine than you currently have. It's roughly equivalent to an FC of 0.1 ppm with no CYA so about 1/5th the amount of disinfecting chlorine as your current 0.5 ppm.

Richard

 

[Poolsean]

Richard or Jason,

What do you think is causing Andy to not be able to shock the combined chlorine out? It's unusual for this not be able to be oxidized out by shocking.

 

[Poolsean]

Sorry Richard, forgot to answer your question about the ORP. The ORP is measuring the mv of the water and not FC levels. The ORP setpoint is adjustable but not calibratable (sp?).
If is continually high with a low FC reading, the ORP sensor may need to be cleaned.

 

[chem geek]

So if there isn't a calibration procedure for the ORP sensor, then the ORP mV target level may have to be set a little lower after the CYA is added. It all depends on what the measured ORP becomes after 20 ppm CYA is added and what FC the controller then tries to achieve. So the key will be to set the ORP to some setpoint that has the controller try an achieve an FC of 2 ppm after the CYA is at 20 ppm. I don't trust the mV reading of any ORP sensor in terms of its absolute value. Different sensors measure the same water and get different values (I have many examples of that) so it's fine for control of FC (assuming pH is relatively stable) but it's not so good as an absolute measure.

As for the Combined Chlorine, it is not unusual for this to persist in an indoor pool. The lack of exposure to UV radiation from sunlight is the primary reason the CC is higher as CCs are broken down by UV. However, I think there is another reason in this case since some CCs are formed at higher disinfecting chlorine levels. For example, in the breakpoint of ammonia, more disinfection by-products such as dichloramine and nitrogen trichloride are formed when the chlorine level is higher and these get measured as CC (and they smell bad, too). I've got a spreadsheet that calculates this and it roughly corresponds to the disinfecting chlorine concentration so 2 ppm FC with 20 ppm CYA will produce roughly 1/5th the amount of dichloarmine and nitrogen trichloride compared to 0.5 ppm FC with no CYA. The main downside to the CYA is that the breakpoint of the monochloramine takes longer, but it's still less than an hour. The pool should remain uncovered after use for at least 30 minutes if not an hour so that the breakpoint reaction can more readily occur (it outgasses nitrogen).

If some of the CC is indeed the aforementioned chloramines, then they are volatile and can be removed through more rapid air exchange, but that means having the pool be uncovered more often. I would recommend first getting the CYA in the pool, both to reduce corrosion and to reduce the rate of production of disinfection byproducts. Then after things are stable, have the cover off the pool and have strong air flow in the pool room bringing in fresh air and exhausting the pool room air for a few hours with the pool pump running (aeration of the water by turning up the jets may also help though that will make the pH rise). Unfortunately, this gets expensive in terms of reheating the room, but it may reduce the CCs. Another option would be to use UV lamps on the uncovered pool.

By the way, 0.6 ppm CC is not terrible, especially for an indoor pool, and I think could be reduced through the above methods to something tolerable under 0.5 ppm. What is somewhat unusual is having an SWG and still seeing the combined chlorine since usually the superchlorination removes it, but again I think the lack of good air circulation (since the pool is usually covered) combined with the much greater production of DPBs overwhelms the SWG (remember that it takes many turnovers for the pool water to get exposed to the superchlorination). We'll see what happens once some CYA is put into the water. This is one of those areas where theory may not match real-world, but I'm hoping that it does.

Richard

 

[dschlic1]

The relationship between pH, ORP and chlorine residual is highly unlinear, if fact it is exponential. Small changes in pH produce large changes in ORP for a given chlorine level. temperature also plays a role.

However it is interesting to note that many authorities state that what is important is the ORP level, with a range between 600 and 700 being recomended. The reason being that ORP is suppose to measure the oxidation power which is what destroys organic matter.

 

[chem geek]

Yes that's the theory. I don't want this thread to get hijacked so look at this post for some info on different ORP sensors. Since I wrote that a while ago, I've found numerous additional examples of mismatches, the most recent being between the ORP of automated controllers (from different manufacturers) vs. a single portable Oakton ORPTestr10, Double Junction tester. Measurement pairs (a subset, since there were 127 measured pools with both sets of ORP data) were as follows with the Oakton first: 435/762, 702/550, 783/690, 886/701. Many measurements were closer, but few were within the 20 mV or so that represents a rough doubling of disinfecting chlorine concentration. And yes, there is a strong dependency on pH and temperature and I've got formulas that track that pretty well even though there are factors to adjust for differences between theory and real numbers. I've pretty much concluded that ORP is OK for control at a given pH and temp, but not so good as an absolute standard except in rough terms (ironic given the 650 mV "standard" for disinfection).

Richard

 

[JasonLion]

Sean, Chem Geek's theory that the pool needs more exposure to the air to reduce CC is plausible. I also wonder if the Metal Magic is adding anything that gets turned into CC. Some of the sequestrants do break down into CC and some don't. I am not sure if Metal Magic does or not.

dschlic1, the Total Control system will normally hold the PH stable within +-0.03 or better, so PH variation is not going to be a significant factor here. Since the pool is indoors I suspect that the temperature is quite stable as well. Also, ORP readings can vary in many ways that are unrelated to oxidation power. For example, adding MPS to a pool will change the ORP reading dramatically without a corresponding change in the germ killing power. ORP readings can also vary significantly between different sensors from the same manufacturer. That makes absolute ORP readings misleading at best. ORP is best used as a relative reading calibrated to standard water testing for each specific pool.

 

[andy]

Thanks for everyones help on this. Here is where I stand now.
Today I went to my local pool store and had them test my water and also test for iron. I will order the Taylor K-1106 Phosphate test kit tonight so I can do that test since my pool store can't.

My readings today using Taylor kit:
FC .4
CC .6
PH 7.2
TA 120
CH 375
CYA 0

Pool stores test using BioGuard Accuscan 2 (test strips that get put into reading machine)
FC 0
Total Chlorine 0
PH 7.5
TA 91
Total hardness 399
CYA 13
Iron 0 pool and 0 fill water(I have well water)
Copper 0
Which test do I go by? Also I'm ready to add the CYA which I have disolved in a 5gal pail

 

[JasonLion]

I would go with the Taylor test. Test strip readers tend to have a low precision, that is they can read significantly high or low on any given try.

The only test which really disagrees is the PH. The rest of them are within the expected precision of the two tests. I am a little concerned about the PH, not because of the test strip reader but because the Taylor test disagrees with the Total Control PH sensor by too much. It can be a little difficult to read the Taylor PH test exactly, but being off by 0.3 is quite unlikely and may indicate that your PH sensor needs to be either cleaned or calibrated or both.

 

[andy]

My last two days PH reading are:

12-13-07
PH taylor kit 7.2
PH total control 7.37

12-14-07
PH taylor kit 7.2
PH total control 7.4