Confused about some of my chemistry levels....

Jump to latest Follow Reply
Gooserider

Gooserider

0
LifeTime Supporter
Feb 25, 2009
211
North Billerica, MA, USA, etc.
As in my sig, pool is ~16.5Kgal, concrete / plaster (not sure how to tell the difference, or if it matters...) Sand filter, SWG, both of which are fairly new, and I'm still learning my way around them...

Swimmer load is fairly low (Me a few times a week) but I get a lot of plant debris, and an amazingly high number of drowned mice in the skimmer. I've been losing a fair amount of water from evaporation, but don't have much loss from splashout or otherwise.

I did a full water test today, with an elderly TFP test-kit, except for borates, where I've found the test strips to be pretty hard to read - I have some, but how much is a guess.... I add about 3 boxes when I open the pool, which I figure should make up for what I lose each fall when pumping it down...

Results -
OTO Cl 5+
pH 7.8
FAS/DPD 4
FC 0
TA 100
CH 270
CYA under 20

I'm using borates, the Compupool SWG says the levels are OK (I can barely taste salt)

A couple of weeks ago (7/10) the pool store tested and showed
FC 5.5 (I have since both decreased the % out on the SWG, and reduced the run-time for the main pump to 6hrs on / 6hrs off)
pH 7.8 (I added about 1/2 gallon of Muriatic Acid)
TA 106
CH 125 (I've added about 10-12lbs of Calcium chloride ice melter)
CYA 36
Salt 3075 (They used some sort of electrical meter for the test, not strips)

The water looks great.... I do have some "water-boatmen" bugs in it, but no other signs of life, and it is crystal clear.

My test results have been pretty consistent, and agree with the pool-store tests (for whatever that's worth) except for the CYA, which is the number I probably have the least faith in from my own tests, and I've felt that way since starting with TFP several years back...

Probably my biggest question is WHY do the suggested levels want the CYA for an SWG pool to be so much higher than they are for a pool that is just running bleach? Per the general chemistry descriptions, my understanding is that its best to have CYA levels that are just high enough to keep the chlorine from disappearing in daylight - why does having an SWG - which should keep the chlorine level better, raise the recommended CYA level? I note that per the Pool School CYA / Chlorine chart, I'd be in great shape if running bleach, but am marginal for an SWG even though that should (per the notes) need LESS chlorine? :confused:

Also, when I've been getting Muriatic Acid this year all I can find is stuff labeled as "safer" that has no Baum rating on the label, and is supposed to be lower fume than the "good" stuff.... Is there any reason not to use this variety - I'm not sure if it's as good at lowering pH, and I don't know what they might have put in it in order to make it "safer" and whether or not it would bother the pool. I've been using it so far, and not seen anything bad, but thought I'd ask...

ex-Gooserider
 
CYA levels are a balancing act between needing to add less total chlorine to the pool at higher CYA levels vs. having a much harder time fighting algae at higher CYA levels. Contrary to what you said, that does not mean "levels that are just high enough to keep the chlorine from disappearing in daylight". For a typical pool that balances out around CYA at between 30 and 50. But a SWG changes both sides of the balance. You want the SWG cell to last longer, so higher CYA levels are better, and you have lower odds of ever having to fight algae, so again higher levels are better. By keeping CYA low you are roughly halving the lifetime of the SWG cell, and making the overall chemistry less stable, i.e. more sensitive to disruption and thus more likely to get algae if something goes wrong. Lower CYA levels also mean more PH drift.

The "safe" muriatic acid is alright to use, but it tends to cost about two to four times as much, or more, though pricing varies.
 
Thanks JL, though I have to say that I'm not getting it... :confused: I look at the chart which says that the more CYA I have, the more FC I need, and that reads to me that I'm needing more chlorine in the pool - though a lower number for a given CYA level with an SWG than if I was doing bleach...

This seems very counter-intuitive when you say that running more stabilizer means longer life from the SWG cell even if I have to run it at a higher level (or am I needing a higher level????)

FWIW, the SWG is on it's second season, and I've been cranking it down slowly (along with my filter pump run time) ever since I opened the pool in order to find out how low I can run it and keep the water OK. Right now I'm running the main pump 12 hours a day (6hrs on / 6hrs off - which was suggested here) and have dropped the SWG to 40% output, or effectively about 20% if I was running the SWG all the time...

Granted my SWG is way oversized (again per advice I got here last year when I was shopping for new plumbing) but it seems to me like I'm hardly putting much stress on it...

ex-Gooserider
 
i feel your pain im still not 100% on this
but the way i understand it is a SWG can add 3-4 ppm FC per day under normal conditions
so you need a higher CYA level to protect what you have
of course at a higher CYA you need a higher FC
with liquid chlorine if you have a bad time and need 5 or more Fc you just pour a little more in
the longer you run your SWG the more it will affect your ph level
i would set your pump time on filtering requirements and then adjust SWG to suit
i run 3 hours@50percent in winter which equal 0.7ppm FC
and 6 hours at 100 percent in summer which equals 3ppm FC
 
The amount of ppm of FC that a SWG can generate is dependant on the SWG output and the size of the pool. For example, if I ran at 100%, 24/7 my SWG outputs 1.45 pounds of chlorine gas per day. In my pool that is 9.7ppm possible per day. The reason to oversize is so that I can reduce my pump run time and SWG output to only give me the ~2ppm that I need.

The higher CYA requires a higher FC level, but you actually lose less to the sun, so less needs to be added daily and thus the SWG works less. The lower FC levels for a SWG at the same CYA is for a few reasons like the harsh environment within the cell.
 
I forget just how I came up with the 6 on / 6 off figure, but I know the recommendation is to have one or two turnovers / day, where theoretically all the water passes through the filter. It was also suggested that more short cycles was better than one long one... Given my old pump and filter I got to the 12 hours / day figure, I forget just how.

My numbers are for summer use only - winter use is none, since the pool is shut down with all the plumbing drained and power disconnected. With my new home-brew control system, I will probably leave power running to the control box just to keep from draining the battery on the RTC module, but the runtimes will be set to all zero and the pumps and SWG unplugged to make sure they don't try to turn on...

In theory the SWG I'm using should be for a 45Kgal pool (the purchasing advice was to get the biggest size available, as it gets more life out of the cell, and the price bump to go up in size is minimal...) so I CAN put a lot of chlorine in if I wanted to, but mostly I don't...

At this point my start-up drill in the spring is to pull the cover off, gag at the green swamp / leaf tea, and dump in about half a carboy of pool-store 12% bleach, and any needed top up water, and start running the filter 24/7 (Ditto the robot with a leaf bag) and the SWG off. After a day or so (and probably at backwashing at least once) I will start testing water and add enough salt to get the SWG into operating range, and get it going at 100% while working on getting the other chemistry under control... (I will probably have to backwash 2-3 more times during this) I takes a week or so but as the pool becomes swimmable, and the water starts looking OK, I keep cutting back on the filter times, and SWG %...

As I said, this setup is new to me, so I'm still learning how to get it working best, will probably be cutting back on the SWG much faster next year, as my experience this year says it looks like I can...

ex-Gooserider
 
jblizzle said:
The amount of ppm of FC that a SWG can generate is dependant on the SWG output and the size of the pool. For example, if I ran at 100%, 24/7 my SWG outputs 1.45 pounds of chlorine gas per day. In my pool that is 9.7ppm possible per day. The reason to oversize is so that I can reduce my pump run time and SWG output to only give me the ~2ppm that I need.

The higher CYA requires a higher FC level, but you actually lose less to the sun, so less needs to be added daily and thus the SWG works less. The lower FC levels for a SWG at the same CYA is for a few reasons like the harsh environment within the cell.
Click to expand...

OK, that makes a little more sense when you put it that way... Will add some more stabilizer, and see what happens.

Looks like that is one of the few things I actually need to get at the pool store - to bad there isn't a lower budget alternative... I know when I was just bumping up my CH levels, the pool store stuff was around $35 for 25lbs, but I got calcium chloride ice melter at the local hardware store for $40 for 100lbs - so I've got a couple years worth of supply AND can take care of my driveway this winter.... (I would have paid even less, but both sLowes and Home Despot were out...)

ex-Gooserider
 
Gooserider said:
I forget just how I came up with the 6 on / 6 off figure, but I know the recommendation is to have one or two turnovers / day, where theoretically all the water passes through the filter. It was also suggested that more short cycles was better than one long one... Given my old pump and filter I got to the 12 hours / day figure, I forget just how.
Click to expand...
This is based on an old rule of thumb that turns out to be wrong. You don't need anywhere near that much pump runtime.
 

Enjoying this content?

Support TFP with a donation.

Give Support
For the critters in the skimmer, I had the same problem. For the 3+ years I've owned my pool I ALWAYS had frogs, lizards and the occasional bird. Gross, I hated it. This year it was like a frog a day! Once I even had a huge bullfrog enjoying the pool, the kind that when it's swimming it's like a foot long, but I managed to scoop him out when he came up for air. (I live near a river in Louisiana, a least no alligators so far!).

Anyhow, I bought a couple of "Frog Logs" online. They are little inflatable bags that float in the water snug up to the pool wall, held in place by little sandbags on the surround. Since I put 2 in my 18k gallon pool 2 months ago, not one critter in the skimmer! Not one. I'm amazed. On more than one occasional I've seen a little froggie swimming around the edge looking for a way out, and once they run into the FrogLog, they climb up on it and jump out. People use them for mice too.

Frog log in the pool:
frog log.jpg

Me doing some frog hunting at night; frog with beady eyes taking advantage of an escape route:
frog on the frog log.jpg
 
Thanks for the comments... I haven't had any eatin' size frogs in the pool :cry: :p just the little ones... Also one or two baby snapping turtles, but an amazing number of mice - though it varies a lot, I can go for weeks without any, and then I'll have a stretch of 1-3/ day...

Those frog-legs look like a neat idea, though I don't know how well they would get along with the pool robot - the bot seems to like getting tangled with anything left in or near the pool... Before we got the Polaris, I experimented with a gizmo called a "Pool Gobbler" that actually worked quite well for what it was - a float with a hose that plugged into a return in place of the usual "eyeball". The hose directed the water through a big hole in the float, and into a mesh bag. It did quite a nice job of getting all the floating leaves and other plant droppings off the surface. For the price (IIRC around $20 or so) it was well worth it... But I found that the Polaris would eat the bag at every opportunity, so I had to take it out after having to separate the two 3 times in three days...

I've dumped in about 28 oz of stabilizer, may add about the same again in another day or so, as the Pool Calculator seems to say I need 50-60 oz. to get me up to a CYA of 60. If I'm understanding the way the chemstry should work, then I will see my FC go up as the stuff dissolves, until I cut back on the SWG output level and / or reduce my pump runtimes. (Speaking of which, JL, if I don't need as much runtime as the 6 on / 6 off that I have right now, what would you suggest, or is there a reference on this in Pool School or elsewhere?)

I know I can get stabilizer at other places besides the pool store, but the mentioned prices aren't actually that much less than the PS prices... Seems to me that no matter where you get it, it still says "Pool Supply" on the label so they bend you over for it... I was thinking more in terms of a complete "substitute" product like Ice Melter instead of Pool Calcium, or water softener salt instead of pool salt, etc... Even so it isn't that big a deal, as I do like being able to occasionally use the free water testing service at the pool store as a double check on my own testing - and I figure that if I'm getting their "free" tests, I ought to at least occasionally get something from them, and aside from stabilizer and 12% chlorine, there isn't much they carry that I need to buy any more...

IMHO if you are going to use the Pool Store testing service, it is important to look at how they do the tests - I've had some stores that just use the same strips they sell (sometimes with a fancy automated reader) which doesn't seem very useful. OTOH I have seen some stores (like the one I'm using now) that have some sort of titration test with pre-filled reagent cartridges and an automated reader that seems to me like it might be more precise than counting drops while sitting at poolside, and trying to judge just which drop was the last one to cause a color change...

The pool store tests are not a substitute for the TFP recommended kits and procedures, but I think they make a good double check - if we both come up with the numbers in the same general range, then all is well - if not, then it tells me I have a problem with either my equipment / technique, or something else that needs attention....

ex-Gooserider
 
Ran some more tests today, after adding some stabilizer, though it hasn't all dissolved yet... My TFP testkit CYA is now up to around 35 (from under 20) and the FC level had also increased from 4 to 6.5 - so I've cut the pump run time down to 5 hours on / 7 off, and the SWG from 40% to 30%...

As a side note, when I am using the pool calculator, the goal levels in the description area seem to match the choices for pool type, chlorine source, etc. but the numbers in the "target" box don't seem to have anything to do with the goal levels. I don't know where those numbers come from. Also, even if you have a "Current" value that is within the goal range, if the target and current boxes don't match, you still get told to do stuff to get to the target.

The PC is a wonderful tool, but it would seem more intuitive to me to have the "target" be a range - presumably set by the goal recommendations, and if within the range have some sort of "It ain't broke, don't mess with it!" message...

ART
 
You are supposed to manually input your desired levels in the TARGET column. It is not automatic. The tool just tells you how to make the changes you input.

There are goals that show a suggested range based on the info at the bottom, but you have to decide what level you want.
 
What he said about the manual entry of the "Target". The goal will usually be a range (7.2 to 7.8) but through experience and experimentation you might find a number or area in that range that works best for you and your pool.

There is nothing wrong with running your pump more than too little but you might be able to save some money if you cut back a bit more on daily run time. The Pool School article says that a single speed pump 4 hours and dual speed running on low 8 hours.
This is from Pool School - - > http://www.troublefreepool.com/content/152-determine-pump-run-time
 
kiss4afrog said:
What he said about the manual entry of the "Target". The goal will usually be a range (7.2 to 7.8) but through experience and experimentation you might find a number or area in that range that works best for you and your pool.

There is nothing wrong with running your pump more than too little but you might be able to save some money if you cut back a bit more on daily run time. The Pool School article says that a single speed pump 4 hours and dual speed running on low 8 hours.
This is from Pool School - - > http://www.troublefreepool.com/content/152-determine-pump-run-time
Click to expand...

I am fine with the way the PC works now, but it just seems like it would require less manual entry if it supported a range and set that per the goal levels.... Not a big deal, just file under the "would be nice" list, and drag it out for consideration if working on the next revision...

Thanks for the link to the Pool School article - I hadn't seen that one before, and it does help a lot... As I mentioned, I had been running 6 on / 6 off based on the older 1-2 turnovers a day suggestion, but I certainly have no problem with cutting back on the time if that is safe.... I suspect my time might vary some depending on just what kind of **** the trees are dumping in the pool this week, :pth: but my home-built controller makes changing the run time pretty painless, just opening the box and flipping the right switches....

Right now I'm experimenting - just going at it from the opposite end than what the article suggests - instead of starting with a minimum time and increasing until I get good enough results, I'm starting at the maximum (Which I REALLY NEED when opening the pool!) and cutting down until it stops getting the job done reliably.... A slow process this summer, but will be a lot faster next year if I know where I want to end up...

Side question - Since I will ALWAYS need to add stabilizer (along with salt and other chemicals) when I open, and it really isn't great to use the SWG to make all the chlorine I need to vanquish the green slimy leaf tea, is there any reason NOT to use sticks / tablets / pucks for the first week or so while beating the chemistry into submission? I also would be using bleach, but since that goes away pretty fast when the CYA is also low, it seems to me like it would be good to have a fairly steady "makeup supply" that also increases my CYA....

ex-Gooserider
 
The chlorine goes away quickly from the sun when the CYA is low, regardless of what the source of the chlorine was. There is no problem using those products if you understand what they do and need the added CYA. Although if you are having to SLAM, then you will also have to use bleach to get the FC level up quickly.
 
jblizzle said:
The chlorine goes away quickly from the sun when the CYA is low, regardless of what the source of the chlorine was. There is no problem using those products if you understand what they do and need the added CYA. Although if you are having to SLAM, then you will also have to use bleach to get the FC level up quickly.
Click to expand...

Sort of what I figured... I was thinking in terms of dumping in a bunch of sticks / pucks / tabs (AFAIK, its like pasta - all the same stuff, just different shapes :p ) along with a gallon or so of 12% when I open in order to help keep the FC up without having to be there to keep dumping in the bleach, and at least get a start on pushing the CYA in the right direction...

I am mostly "flying blind" on the chemistry for the first few days after I open, as the water is IMHO to raunchy to test - how do you see a color change when the water is brown??? I just dump in what I'm pretty certain I'll need from previous experience, and figure if the water is clearing up at all, I'm making progress. After the water gets at least semi-clear I start worrying about getting actual numbers and making more precise adjustments.

ex-Gooserider
 

Enjoying this content?

Support TFP with a donation.

Give Support
You must log in or register to reply here.
Thread Status
Hello , This thread has been inactive for over 60 days. New postings here are unlikely to be seen or responded to by other members. For better visibility, consider Starting A New Thread.
Top Bottom
Back
Jump to latest Follow Reply