nodules where the tile meets the pebble?

[g8tors]

This is my first post and its something that has been bothering me for the past year. I have a 18k gallon salt water in ground pool. the old pool was regular gunite and had been painted by previous owner. I've been getting these white nodules around the pool where the tile meets the pebble. 3 months ago i did a partial drain and using a 50/50 mix of muratic acid and water dissolved/scrubbed the away. looked great but now they are coming back. i think it may be calcium being pulled out of gunite there at the border? Should this border be sealed? pool looks great and this is the only area where these nodules appear. there is NO scaling anywhere in the pool or the salt cell (hayward 40K)

Any help would be great.
salt 3200
ph 7.6
alc 120
hardness 300 or so, depends on who you ask
I use 8oz of metal out every month, seems to help but not enough

dave

 

[Charlie_R]

Welcome to TFP!

A couple of questions:

First, how are you testing. If those numbers are from a pool store, they are likely to be wrong. Your best bet is to purchase your own test kit. We recommend the TF-100 from http://tftestkits.net or the Taylor K-2006. Both of these are FAS-DPD drop based kits. No other kits will measure as well or as accurately.

If those are pool store numbers, what kind of testing are they doing? Test strips or computerized testing? Of the two, the computer will be closer, but still is likely to be wrong.

I suspect that your CH number in particular is wrong, and could be quite a bit lower than is being reported. If this is true, then those nodules would be calcium being leached out of the grout/thinset.

 

[g8tors]

i guess i should have did a search first because there is an excellent thread to this very problem, with 1 exception. looks like the issue is the bond between the tile grout and the pebble finish. The pebble potion of the pool is fine, no nodules anywhere. my only nodules are at the seam between the grout and the pebble finish. i wonder if some sort of sealer would work along the whole perimeter of the pool would work.

Charlie, i use a Taylor test kit. I also think you are 100% right about the grout. This is my 3rd pool home but first time ever seeing issue like this. I've always maintained my own pool and get water tested every 2 mos at the store to see what product they want to sell me that i don't need

 

[onBalance]

Yes, you are correct. There is a slight separation between the pebble plaster finish and the tile. Remove the nodules again as you did earlier, and using any type of water-proof sealer should plug the cracks and stop the calcium nodules from re-occurring. This situation has nothing to do with the water chemistry balance. If the pool water was CSI aggressive, then no nodules would form.