SWG with crazy hard water and variable speed pump

[dndntsd]

Hi everyone. I have a new pool, 35,000 gal, in ground, concrete/tile. I'm looking at getting a SWG like the Jandy Aquapure Ei but I have a few questions I hope you can help me with...

I'm in the country so I need to fill the pool with my well water which has a calcium hardness of 1,100ppm. No, that's not a typo. I'm in the Yucatan in Mexico, the ground is all limestone and the water is crazy hard. (also, the water has 3,200ppm of saline - just about right for the SWG) So, question 1 - will the calcium cause scale or damage the generator? How often will I need to replace the cell?

I have a Hayward variable speed pump which leads to question 2 - Is there a minimum flow rate for these SWGs? Do they work well with variable speed pumps?

The cost of power down here is very high so, question 3 - how much power do these units use? I can't find the info on the websites for the generators.

Thanks in advance for your help.

 

[Casey]

That's some very high CH and it will scale your pool and cell. Have you looked into reverse osmosis? It will basically clean the water of high CH and CYA.

 

[ping]

You will be able to use a SWG but you will need to keep a close eye on the pH. You will need to make sure it stays in the 7.2-7.5 range and also the TA will need to be on the low side 60-70. You will also want to look into adding 50 ppm borates as this will help with scaling issues inside the cell.

I don't recommend the Jandy Aquapure Ei as it has been discontinued in the states and it is small for your pool size which means it will have to run more than other sized cells. Also, it has a high flow rate requirement compared to most other SWG brands. Look for a brand that has a rating around 60,000 gallons.

If you don't want to go the SWG route, search the forum to learn about a system that injects liquid chlorine such as a Stenner pump. With a Stenner pump, pump run time will not be an issue as you can inject enough chlorine in a short run time.

 

[salinda]

I have been running an SWG with a similar very high CH for years. We are in a drought in California and I am uncomfortable with drain and refill to lower CH (it's illegal right now anyway). My pool looks beautiful. I have had to replace cell about every 5 years, which is well within normal limits. Just find an SWG which is easy to maintain. You will have to add acid to the pool weekly and rebalance the salt and CYA after rainy season if your weather cycles as it does here.

People warn about scale but my plaster is in beautiful shape with the methods I have learned here. I'm not crazy about it. Sometimes my ph gets a bit high (7.9-8.0) but I have not experienced scaling except on the cell yet. My plaster is well beyond what MOST contractors will tell you it should last as it is well over 10 years old and smooth and comfortable. I use the excellent Pool Calc iphone app to help me figure things out and then I really eyeball from there. If it says to add about 2 quarts of acid, I add muriatic acid (HCl) at the return in a thin stream until I am holding the gallon roughly horizontal. I figure that's 1/2 gallon and I'm good. When I have been anal about it and remeasured ph after the addition, the math was almost spot on.

I am right now waiting on a salt cell replacement and I have to add about 2 gallons/week as my pool is in full sun and it is hot.

 

[zamazing]

The cost of power down here is very high so, question 3 - how much power do these units use? I can't find the info on the websites for the generators.

Thanks in advance for your help.

In practice, my Hayward T-15 Cell (designed for a 40K Gallon pool) draws between 6 - 7.5 Amps of current at around 28 Volts when its generating chlorine. Assuming another 10-15% for the panel and power supply efficiency (another 1 A), then you're looking at a worst case 8.5 A at 28 Volts = around 240 Watts when generating and maybe 25 Watts when idle.

 

[chiefwej]

Although my CH isn't as high as yours, mine is high and we have extremely high evaporation rates. Last year my CH was well over 1,000 all summer. It can be managed without having scale either on the pool or in the SWG cell.

You have to use the Pool Math calculator to carefully monitor and control the CSI (Calcite Saturation Index). The CH level only tells you how much calcium is in the water. The CSI tells you if that calcium will stay in the water or perciptate out as scale. There are several factors (CH,TA,temp, pH, etc) that effect the CSI. Of these the one you have the most direct control of is pH. Ping is right that you will need to keep a close eye on the pH, because that's how you will control the CSI. Lowering the TA is useful in that it helps combat a rising pH, which is always an issue in a SWG pool. Adding 50 ppm borates could be useful in further buffering pH rise. The higher the CH, the more of a balancing act it becomes. With the high levels you have it will be like walking a tight wire, but with diligence and care, it can be done.

I also have the Hayward AquaRite T-15 unit and I highly recommend it. It gives you control of the output in one percent increments and has good diagnostic information on the control panel. Mine has been in service for ten years. I replaced the cell after 7.5 years and had to replace an input resistor (15 min with a soldering iron and $2.50 cost). There are lots of this unit in use, so information and advice is readily available. The unit is affordable online at less than $1,000 U.S. When the cell does fail (as mine did after 7+ years of service) a new one is less than $400 U.S. That made my cost for chlorine less than $56 U.S. per year.

 

[dndntsd]

Wow, thank you all for the information. This gives me something to chew on. Do you guys think there is a benefit one way or the other between a SWG and a chlorine injection system?

Not sure how I'll go yet - the pool is very new so It'll take some time to see how much chlorine I use etc. Lots more research I guess.

- - - Updated - - -

Oh yeah, I looked into a R.O. system for the whole house... it was going to cost aroung $15,000 for the whole setup. So, I don't think that is an option!

 

[chiefwej]

A water softner on your fill system can help combat CH rise, as replacement water is added.