Why?

[Philo]

TFP is one of the very few who recommend the Calcium level to be 350-450 with a SWG in a plaster pool. Most are much lower.
How come?

Thanks

 

[CajunGuy]

TFP is one of the very few who recommend the the level to be 350-450 with a SWG in a plaster pool. Most are much lower.
How come?

Thanks

Are you referring to the Calcium Hardness?

 

[pinguy]

The NPC and most SWG manufactures state 200-400. I'm not sure why the charts here recommend a slightly higher level for SWG users (someone will chime in), but the difference is pretty negligible if pH is maintained properly.

 

[ping]

If the CH is kept on the higher side, the TA can be kept lower to help prevent the pH from rising. These numbers will help maintain the CSI in range.

 

[CajunGuy]

I'm interested in this too. My CH was 170 and I have a SWG gunite/plaster pool. Someone recommended bumping it up some to at least 250 so I don't leach Calcium from the plaster. The previous owner must have been adding Calcium routinely bc he left a big 5 gallon bucket of it. I had some scaling around my waterfalls (moderate amount) and minimal amount on the tile line, but I don't know if that can be attributed to the previous owners letting the pH routinely become too high. It was at 8.0 when we first moved in about a month ago. Since then I've brought it down to 7.4 and now I'm questioning whether or not I should up the CH?

 

[ping]

What is the fill water CH and how often do you need to add fill water? If it is high enough, the pool will have 200 CH soon enough. For now, keep the pH 7.6/7.8 range.

 

[pinguy]

I'm interested in this too. My CH was 170 and I have a SWG gunite/plaster pool. Someone recommended bumping it up some to at least 250 so I don't leach Calcium from the plaster. The previous owner must have been adding Calcium routinely bc he left a big 5 gallon bucket of it. I had some scaling around my waterfalls (moderate amount) and minimal amount on the tile line, but I don't know if that can be attributed to the previous owners letting the pH routinely become too high. It was at 8.0 when we first moved in about a month ago. Since then I've brought it down to 7.4 and now I'm questioning whether or not I should up the CH?

The thing that matters with preventing calcium scale/plaster damage is keeping CSI below .6 and above -.6. The recommended levels are designed to keep you within this range.

You can calculate your exact CSI with pool math by entering pH, TA, CH, CYA, Temp, Salt and Borates (if you have them).
http://www.troublefreepool.com/calc.html
Pool School - Calcium Scaling

That is all a bit beyond the "just getting started" category, but you don't really need to worry about calculating CSI if you stick to these guidelines: Pool School - Recommended Levels

I think I can answer the original question in this thread though. Salt and CH have opposite effects on CSI - the extra CH is to balance out the added salt with SWG users.

 

[jblizzle]

If the CH is kept on the higher side, the TA can be kept lower to help prevent the pH from rising. These numbers will help maintain the CSI in range.

This is exactly what I was going to suggest was behind the reasoning.

In reality, you can not keep tight control on the CH as it will usually constantly rise due to evaporation (unless you have a lot of rain). So you need to compensate with the pH level you maintain to keep the CSI in range.