UV systems prevent algae growth?

[Pcmaker]

This is for a pool for the hotel I work at. We use 3" trichlor with IPS M920 automated feeders using ORP to add/stop chlorine going to the pool. We set it around 650-720, depending on the free chlorine levels.

Free Chlorine is always good. Around 5, pH is always around 7.6-7.8, Total Alkalinity is around 110. Cyanuric acid is around 50. It's heated to 87 degrees, 38k gallon pool. 125 GPM filtration on average using a Triton II sand filter.

The phosphate levels are always high, we keep adding phosphate remover on weekly basis. The pool just happens to be in a "breezeway" where we have 20 palm trees, along with some bushes and random plants. A slight breeze makes the area very windy.

My question is, will adding a secondary disinfectant, specifically a UV system, prevent algae growth? I've read up on it and it seems to work, but I was wondering if anyone has had any experience dealing with them?

 

[ajw22]

Is this pool indoors or outdoors?

UV systems are helpful on indoor pools to burn off CC's that the sun does naturally for outdoor pools.

UV does little to nothing to sanitize the water. FC of around 5 is not adequate for CYA 50. See [FC/CYA][/FC/CYA]. You need to maintain CYA 6-8 and not have FC fall below the minimum of 4. It is likely the FC is falling below 4 during the day.

My understanding is ORP systems are not reliable with CYA above about 30. Using trichlor I think you will need to monitor the CYA and drain the pool occasionally to keep the CYA down for your ORP system to operate properly.

 

[Pcmaker]

It's an outdoor pool. We check the water every morning for free Chlorine and it stays pretty constant with the new automated system

 

[tim5055]

As Allen said, UV is almost useless for outdoor pools as they get plenty of free UV from the sun.

The problem is eye with your system is that unless you keep the CYA low you will begin to get invalid ORP readings as the CYA. increases. Additionally, increased CYA (your tabs are almost 50% CYA) requires higher and higher FC levels to offset the CYA.

 

[Jimrahbe]

Pc,

I can only assume that you asked the question because you have been getting algae.. If so, the reason is because your FC is not high enough for your CYA level.

If this is true, your only option is to increase your FC or decrease your CYA.

If you are using 3" tablets, then your CYA should be increasing a little each day.. ORPs do not like high CYA, so I have a hard time believing that things are fine at your end.

How do you test your FC each morning?? How are you testing your CYA levels?

While your here, you might also do a search on what we think of phosphates.. Following our advice would allow you to never use phos-free again.

Thanks,

Jim R.

 

[tim5055]

Another point to keep in mind is that a hotel pool is considered a commercial pool in most jurisdictions. Local and or state health regulations may have limits of FC and CYA.

While our method of pool care is good, it does not play well with some states commercial pool regulations.

 

[ajw22]

It's an outdoor pool. We check the water every morning for free Chlorine and it stays pretty constant with the new automated system

OK, let's work through this.

You check the the water every morning and have a FC of 5. The [FC/CYA][/FC/CYA] tells us at CYA 50 you need a minimum FC of 4. You can lose 2-3PPM during the day from the sun and more with a high bather load consuming CL. At CYA 50 with a FC of 5 you don't have enough headroom and likely lose more than 1 PPM before your ORP system can respond. Plus the high CYA is giving invalid ORP readings.

So while your FC is looking okay in the morning it is likely falling below the minimum FC for your CYA during the day allowing algae to take hold.

You need to get your morning FC up to 6-8 or lower your CYA. And even FC of 6-8 may not work for you as TFP recommendations are for residential pools with low bather load.

 

[Pcmaker]

Pc,

I can only assume that you asked the question because you have been getting algae.. If so, the reason is because your FC is not high enough for your CYA level.

If this is true, your only option is to increase your FC or decrease your CYA.

If you are using 3" tablets, then your CYA should be increasing a little each day.. ORPs do not like high CYA, so I have a hard time believing that things are fine at your end.

How do you test your FC each morning?? How are you testing your CYA levels?

While your here, you might also do a search on what we think of phosphates.. Following our advice would allow you to never use phos-free again.

Thanks,

Jim R.

I use the Palintest pool test kit for the Free Chlorine since it's a lot more accurate and the Taylor K2006 DPD test kit for CYA. I also sometimes double check the free chlorine with the DPD test kit.

Another point to keep in mind is that a hotel pool is considered a commercial pool in most jurisdictions. Local and or state health regulations may have limits of FC and CYA.

While our method of pool care is good, it does not play well with some states commercial pool regulations.

CYA can't be over 99 and FC can't go over 20 PPM. pH has to be between 7.2-7.8, TA can't go below 80 or over 120. That's the local regulations.

OK, let's work through this.

You check the the water every morning and have a FC of 5. The [FC/CYA][/FC/CYA] tells us at CYA 50 you need a minimum FC of 4. You can lose 2-3PPM during the day from the sun and more with a high bather load consuming CL. At CYA 50 with a FC of 5 you don't have enough headroom and likely lose more than 1 PPM before your ORP system can respond. Plus the high CYA is giving invalid ORP readings.

So while your FC is looking okay in the morning it is likely falling below the minimum FC for your CYA during the day allowing algae to take hold.

You need to get your morning FC up to 6-8 or lower your CYA. And even FC of 6-8 may not work for you as TFP recommendations are for residential pools with low bather load.

With this system, if we keep up the minimum FC in relation with CYA, we generally don't have to worry about phosphate levels?

 

[tim5055]

If you have a Taylor K-2006 it actually has a FAS/DPD FC test which we have found to be the most accurate out there. It will test FC to a max of 50 in either .2 or .5 increments.

The Taylor K-2005 has the DPD (color match) FC test.

Yes, once the algae is eradicated if you maintain the correct FC to CYA ratio all the time phosphates are a non issue. The pool stores will tell you that phosphates are algae food and you must eliminate it. We counter that you can have the best buffet of food going, but if it’s in a room full of chlorine no one can survive to eat it.

What is your pump schedule and when is chlorine being added to the water? My fear is that you are testing the water in the morning and the FC is fine but as the day goes on with UV from the sun (UV consumes chlorine) and bather load you are dropping too low in the afternoon. The chlorine being added overnight brings it back to 5 making it look this everything is fine.

The best way to tell if you have a low level algae bloom happening is to conduct a Overnight Chlorine Loss Test using the .2 on the FAS/DPD test kit

 

[Pcmaker]

If you have a Taylor K-2006 it actually has a FAS/DPD FC test which we have found to be the most accurate out there. It will test FC to a max of 50 in either .2 or .5 increments.

The Taylor K-2005 has the DPD (color match) FC test.

Yes, once the algae is eradicated if you maintain the correct FC to CYA ratio all the time phosphates are a non issue. The pool stores will tell you that phosphates are algae food and you must eliminate it. We counter that you can have the best buffet of food going, but if it’s in a room full of chlorine no one can survive to eat it.

What is your pump schedule and when is chlorine being added to the water? My fear is that you are testing the water in the morning and the FC is fine but as the day goes on with UV from the sun UV consumes chlorine) and bather load you are dropping too low. The chlorine being added overnight brings it back to 5.

The best way to tell if you have a low level algae bloom happening is to conduct a Overnight Chlorine Loss Test using the .2 on the FAS/DPD test kit

Pump runs 24/7 along with the automated feeders, it feeds Chlorine when the ORP falls below the set point

The ORP shows well above the setpoint when I come in early in the morning at 5am, but it lowers to set point levels when the sun comes out before noon.

 

[tim5055]

Pump runs 24/7 along with the automated feeders, it feeds Chlorine when the ORP falls below the set point

The ORP shows well above the setpoint when I come in early in the morning at 5am, but it lowers to set point levels when the sun comes out before noon.

You need to conduct an Overnight Chlorine Loss Test to see if there is algae hiding. But, as I said you need to use a FAS/DPD test to get the .2 discrimination to catch it.

But, that night you will have to turn off the pump/feeders just after sundown and exclude swimmers that night to get a valid test. As chlorine is consumed by both UV and organics in the water, this test eliminates the UV (starting the test after sundown and retesting before sunrise) and limits the FC drop to just organics. A FC loss of more than 1 will indicate algae in the water.

 

[cfherrman]

Figure out if local regs allow hand feeding of chems.

With it being a outside pool orp is probably a waste if money

 

[Pcmaker]

I dumped 7 gallons of liquid Chlorine yesterday and that still didn't clear it up. I wonder if it's something else.

 

[tim5055]

I dumped 7 gallons of liquid Chlorine yesterday and that still didn't clear it up. I wonder if it's something else.

A one time addition of chlorine seldom if ever cures an algae outbreak. You need to follow the SLAM Process directions to accomplish a total eradication.

I didn’t notice any indication of something that needed to “clear up” in your previous posts.

What exactly are you seeing?

 

[cfherrman]

And your test results from Taylor 2006

 

[Pcmaker]

It's cleared up now. The CYA goes up quick in the pool. I have to backwash and fill a lot every day to keep it low.

From what I've gathered with ORP, the higher it is, the more effective free Chlorine is. I used to keep it at 620 ORP, I'll bump it to 700 and see if that makes a difference, along with keeping CYA as low as I can get it.

 

[wogster]

It's cleared up now. The CYA goes up quick in the pool. I have to backwash and fill a lot every day to keep it low.

From what I've gathered with ORP, the higher it is, the more effective free Chlorine is. I used to keep it at 620 ORP, I'll bump it to 700 and see if that makes a difference, along with keeping CYA as low as I can get it.

You need to get rid of the tabs, they are adding CYA and chlorine, and that messes up your automatic feeder which should be set up to a pump that feeds liquid chlorine. An ORP of 620 is too low, check regulations, because I think it needs to be higher.... ORP is a not that accurate for seetings anyway because a lot can affect it, CYA, TA, pH and TC (FC + CC) can all affect it.

 

[Pcmaker]

You need to get rid of the tabs, they are adding CYA and chlorine, and that messes up your automatic feeder which should be set up to a pump that feeds liquid chlorine. An ORP of 620 is too low, check regulations, because I think it needs to be higher.... ORP is a not that accurate for seetings anyway because a lot can affect it, CYA, TA, pH and TC (FC + CC) can all affect it.

I wish we can use liquid chlorine like every other large public pool, but we don't have the space for it.

Checked the CYA this morning and it was at 100. I think I'll backwash every day to keep it under 50 and keep my free Chlorine to 7.5. I think taht should do the trick in keeping algae from blooming again.

 

[cfherrman]

Your orp number is useless at that cya

Triclor tabs are unsustainable, you either will have constant problems or switch to bleach

 

[ping]

You need to drain enough to get the CYA below 30 so your ORP has a chance to properly work.

Once the CYA is at or below 30 then you have a choice to make on how to add chlorine. If you want to continue using pucks you will need to replace a lot of water more often than you have currently been doing.

Your other options are liquid chlorine or SWG both of which can be automated. You might have the best success with ORP and liquid while keeping the CYA at 30.