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Next Water Change - Ideal Setup


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Have been running on the same water now for about 4 months using the dichlor then bleach method.  It has been working well over the last 2 water changes, but I do find I have to knock the pH down a little more than I would like.  My existing setup has been:

TA: 70-75

ph: keep between 7.6 and 8 with 7.8 as my happy place

CH: 160

CYA: 30

BOR: 40

I will be doing a water change in the next few weeks before the weather gets too cold and want to setup for a lower TA next time to slow the pH rise.  Note that my well water is nearly devoid of TA and CH so I have a fairly easy time to get them to where I want.  Here is what I was thinking from the pool calculator:


This setup should keep me in the CSI sweet spot for pHs between 7.6 and 8.  Any thoughts on whether these are good targets?  Is a CH of 200 a bit too high?

@waterbear would appreciate your input.



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On 11/9/2021 at 4:29 PM, dashmer said:


This setup should keep me in the CSI sweet spot for pHs between 7.6 and 8.  Any thoughts

Is your spa plaster? If it's not and is a standard acrylic shell then why are you working about CSI? Keep your calcium above 130 and under 200 to minimize foaming,  TA 60 or 70 if your pH stays stable, borate 30 to 50, CYA at 30, and keep the pH in the 7.7 - 7.8 sweet spot (try to keep PH in the range of 7.6 to 8.0) and main your FC in the 3 to 6 ppm range. When you have combined chlorine higher than 1 ppm then shock. Don't make your water balancing harder than you need and most importantly,  it's a hot tub, not a science project so enjoy it.

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CSI stands for calcium saturation index and this determines whether the water will deposit calcium as scale or dissolve calcium from a plaster surface and cause pitting and other problems. With an acrylic spa obviously there is no plaster to dissolve so running a negative CSI is perfectly fine. However, scale is a problem for all surfaces so you don't want to run a strongly positive CSI. The numbers I gave you will keep your water in a range that will not deposit scale since the TA and CH are both low. The only reason an acrylic spa needs calcium is to increase the hardness enough to help prevent foaming. Soft water foams more readily than hard water so we want enough hardness to prevent this but not so much that you are likely to have scale precipitate if the pH is high. Somewhere between 130 and 200 ppm is good.

Some people think that you must balance CSI in any pool or spa to protect metal from corrosion but this is in error. There is NO correlation between CSI and metal corrosion. However, low pH IS the main cause of metal corrosion, the second being differential electrical current in the water, which is easily taking care of by installing a sacrificial anode and grounding properly.

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