Question About Meaning of Pool Math Results

[johnsimion]

I have a question about the results of my testing and the CSI index that PoolMath is generating. For several months now my results have been very stable, and today's readings are typical (things stabilized after we narrowed the spa outlet and the pool passed its first birthday). I am using the TFT-100 for everything but the CYA test, for which I'm still using my ColorQ, and that only because whenever I've tested CYA with both that and the TFT-100, I get the same results on that particular test. These are today's test results:
Temp: 64
FCL: 12 (DPD) (this is high because I've been dissolving leftover chlorine tablets to get my CYA up -- now that it is getting warmer, I'll be going back to the SWG and I expect the chlorine levels to drop)
PH: 7.5-7.8 (probably closer to 7.5 than 7.8)
TA: 90 (PoolMath Goal 60-80)
CH: 250 (PoolMath Goal 250-350)
CYA: 56 (PoolMath Goal 70-80)
Salt: 3400 (exactly what my SWG recommends)
CSI: -0.30 (potentially corrosive)

My readings are all either within or near the goals set by PoolMath. The pool is crystal clear, I'm no longer getting the calcium buildup, and generally all appears well. Looking back since January, I see that PoolMath has reported "balanced" three times and "potentially corrosive" twice, so it appears that I am fairly close to being balanced. However, that "potentially corrosive" scares me and I don't understand why. Moving within the PoolMath goals would make the CSI worse. If I was 100% within the PoolMath goals, it would have a CSI of -0.85, "corrosion of plaster likely." What can I do to get my pool out of the "potentially corrosive" range? Or do I just not worry about it? At what point would I NEED to worry about it?

BTW, you CAN increase your CYA level using the chlorine tablets in the strainer. It's just gradual. I have gone from CYA of 32 in January to 56 in today's test without doing anything other than putting a few tablets in the strainer. Since my CYA is now pretty close to the goal, I won't be doing that any more.

 

[jblizzle]

Your water balance is fine. One of the major drivers of the lower CSI is that you CH is a little on low side. You could counter that by keeping the pH a little higher.

We all know that tablets will raise the CYA, we do not recommend putting them in the skimmer as that could damage your equipment unless your pump is running 24/7.

 

[johnsimion]

Thanks. That is a relief. It is just scary when you see the "corrosion" word. I will try turning off my water softener on the feed line for a while and that should increase the CH gradually. I agree about the tablets. I just figured that I had the tablets anyway and that using them would be a controlled way to gradually increase the CYA. I won't be doing that again.

 

[ping]

I wouldn't raise the CH anymore by turning off the softener. The water temp will be increasing soon and that will start raising the CSI pretty quick. The CSI is good at -.3 when you have a SWG as it doesn't build up much scale.

Keep the pH between 7.5 to 7.8 and everything else where it is and your pool will be in good shape. During the winter let the pH stay closer to 7.8.