Boss said "Pool will not turn with high chl lvls!" True?

[wolfman83661]

Hi there,

Got a question on algae and chlorine. I recently took over pool maintenance for the property that I work as a tech at in Tucson. I have no no previous experience with working with pools and thou I passed the pool certification for the city I still did not feel I was a experienced pool tech.
Anyways after about 4 months of maintaining the pool as per my immediate supervisors instructions, which stayed nice and clear and clean, it turned on me over the weekend. Or I assumed it was starting to, there was a slight greenish tint to the water and it wasnt its normal crystal clear to the main drain clean. I started with flushing the pool a couple times, vaccuming it then flushing again a couple times then shocking it with 1 bag (24k gal per pack, pool was guesstimated at 25k or so max) and dumping in 1 gal of liquid chlorine. The next day I repeated the process except I ran out of liquid so I dumped in 1 bag of shock early in the day and 1 in later the day. I did not see any progress at that time till on the 3rd day we got more chlorine in to which I dumped in 2 gallons of liquid and 1 bag of shock (I had found 2 buckets of old shock, the previous days I used the oldest of the old shock, the 3rd day I used the newer looking old shock). The 4th day it was definately clearer, I continued the flushing, vac and 1 bag of shock 2 gal chlorine routine (which was recommened by the big boss). The 5th day it was nearly back to its previous glory and I continued the process for that day and the next 2, then cut down the amount of flushing and lessened the amount of chlorine.
Now from what Ive been told the company policy is keep the pucks in the chlorinator and dump 2 gallons in each weekend day, 2 sat, 2 sun ... seems a bit excessive imo but as I said above Im a bit limited in knowledge atm. The company only wants us to test TC and TA, we only have the test liquids for that and I was told by the big boss (head maint super) that a pool will under no certain terms turn if your TC levels remain high .... but my chlorine levels in my pool have stayed at a constant 5 to 7 max, the TA fluctuates a bit from 7.2 to 7.6 over the period of weeks but ive been keeping that in range with soda ash and acid.
So mainly thats my question, is that true my pool will not turn if the TC stays around 5 and if so why did mine turn, its TC levels never droped below 5.

Thanks for any imput yall have.

[chem geek]

It is not true. First of all, it is Free Chlorine (FC) and not Total Chlorine (TC) that would help to prevent algae growth, but the Cyanuric Acid (CYA) level (aka stabilizer or conditioner) is critically important because most of the chlorine is bound to CYA and relatively inactive. The amount of active chlorine (hypochlorous acid) that kills or prevents algae growth is proportional to the FC/CYA ratio (technical derivation is here. So if you continue to use stabilized chlorine (e.g. Trichlor pucks/tabs or Dichlor powder/granular) then without water dilution the CYA level will climb making the chlorine ineffective against algae growth. Even with an FC of 5 ppm, if the CYA gets to around 100 ppm or so (perhaps lower in pools with lots of algae nutrients, higher in pools lower in such nutrients), the algae can grow faster than chlorine can kill it (unless you raise the FC proportionately or use a supplemental algicide or phosphate remover at extra cost).

The chlorine/CYA relationship has been known since at least 1973/1974 as described in this paper and is further described in additional papers linked to in this post. You can learn much more about how to maintain a pool by reading the Pool School.

Also keep in mind of the following chemical facts that are independent of concentration of product and of pool size:

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by 7 ppm.

So even with a low 1 ppm FC per day chlorine usage, the continued use of Trichlor would increase the CYA level by over 100 ppm in 6 month if there were no water dilution.

Richard

[Me...]

Also you must mean pH, not TA. TA would be more like 100ppm and pH is the 7.2 - 7.6 range. pH and chlorine may be the main chemical levels you will need to be adjusting but as chemgeek indicates there is much more to it. Must be an outdoor pool because I bet your eyes would be bleeding if it was an indoor one.

[nocturnalsheep]

Whether or not your pool will turn while chlorine is high depends on a lot of things. Of course, if this is an outdoor pool, it will be exposed to contaminants brought in from wind and rain and these can be nasty. At the pool store I work at, we had a customer that had an "algae bloom" with a FC level of 9.0. The chlorine demand station we have here reported that the amount of chlorine that would be needed to kill it would be 106 lbs. of burn out 35 (lithium hypochlorite 29%). Your boss obviously is not familiar with swimming pool care. Unfortunately, it is not an exact science. There are so many factors that must be taken into consideration that no formula will be truly accurate.

-Danny

"The Pool Whisperer"

[chem geek]

Danny,

What was the Cyanuric Acid (CYA) level in the pool that had 9 ppm FC with an algae bloom? Was this pool using only stabilized chlorine (e.g. Trichlor and Dichlor)?

Richard