What Sanitization To Use?

[Angel15]

Hi guys, I'm in need of some guidance in what to do about chlorinating the pool I recently was asked to manage. The last person didn't really know much about pools and our state doesn't require you to be certified, and he only used trichlor.

Currently the pool uses Trichlor sticks via an offline feeder (or maybe it's an online feeder, I can't remember the difference) to sanitize. However the CYA is through the roof 100+ easily, and you guessed it a cloudy pool. So I'm in the middle of diluting it to get it a bit more clear. But since all we have is trichlor it's a pretty tough battle. Any suggestions on what to use?

59,000 Gallons, inground indoor, gunite, and heated.

The last test my results were....

FC 5

TC 5

CC 0

Alk 60

pH 7.2

Cal hardness 625

Temp 86

The source water...

FC 0

Alk 60

pH 8

Cal hardness 50

[waterbear]

I assume this is a commercial pool?

First, what are the local health dept. guidelines for pool maintenance? I assume you are in Vermont based on your IP address. All I could find for Vermont was spa/hot tub regulations that are sorely out of date and actually contain a miscopying of what sanitiziers require lower or higher TA ranges by swapping dichlor and sodium hypochlorite into the wrong goups. This indicates that these regulations were drawn up by someone with no actual knowledge of water chemistry or the reason why different sanitizers require different TA ranges! Good new is that sodium hypochlorte (bleach or liquid chloirne) is allowed so I would switch to that for chlorination and stop the trichlor altogether.

Second, why is the CH so high? This could be from the use of calcium hypochlorite in the past (not necessarily a bad thing as long as the calcium hardness is kept in line and the pH is monitored closely) to just plain bad water maintenance in the past and damage to the plaster as a result. All that can be done now is to get parameters in line and make sure the pool surface is not damaged and replaster or acid wash if it needs it.

I suspect that almost all your measured TA is from the CYA present, the actual TA from bicarbonate is almost non existant, and that your calcium saturation index is actually strongly negative at a pH of 7.2. Run your pH a bit higher as a safety factor (7.6) until you get the water under control!

Get the CYA down to about 30 ppm and run the FC at 3-4 ppm. If you develop a problem with persistent CC look into installing a UV unit if the pool does not already have one. Also look into replacing the trichlor feeders with persitaltic dosing pumps for the liquid chlorne. Keep the TA at the low end (70-80 ppm) to minimize pH rise from outgassing of CO2. You will need muriatic acid for pH control with an unstabilized chlorine source but will probably never need soda ash ever again. Keep the pH between 7.4 and 7.8 Occasionally you might need some bicarb to raise the TA but you do not want it over 80 ppm. Keep your CH at around 300 and you should be good to go!

Levels to shoot for:

FC 3-4 ppm

CC 0 ppm

pH 7.4-7.8

TA 60-80 ppm

CH 300 ppm

CYA 20-30 ppm

This levels will keep your calcium saturation index between -.3 and +.3 at a temperature of 86 degrees so you should not have to worry about damage to the plaster or scaling.

Hope this helps and good luck!