Bronze Supporter
Jul 18, 2015
Sarasota, FL
Our 20 year old marcite pool was resurfaced in PebblesStone 5 years ago. We've just started getting a couple of calcium "bumps" and scaling. The outfit that did the pebblestone reports this is "normal" as these surfaces can cure for 5-7 years. They recommend acid washing with the following instructions. Please comment before we begin. Thanks.

In Pool Acid Wash
Adding Muriatic Acid to water lets the aggressive water work on surface
Removing light and floor heads is recommended. Also by-pass older
heaters without Titanium coils.
To start, make sure chlorine level is down to 1.0 or less. Add muriatic
acid to the rate of 1 gallon per 3,000 gallons water to start. Then
maintaining alkalinity level at 20 ppm or lower. Using a sequestrian
product will help in lifting scale and metals from surface.
Leave pump running 24/7. Start brushing surface and cleaning filter
Make sure to keep alkalinity at 0-20 ppm or below.
This is a 7-14 day process as needed. When satisfied, rebalance
chemicals. You might need to dump a few feet of water and refill with
fresh water. Check hardness for this. Over 600 ppm, usually needs
dilution (fresh water).


TFP Expert
Mar 2, 2011
Do you have any pictures?

What are the chemistry readings?

What is the CSI?

The bumps sound like they could be calcium nodules.


Bronze Supporter
Jul 18, 2015
Sarasota, FL
Today's chemistry 1-15

FC 6.0
CC 1.0
pH 7.2
TA 60
CH 350
CYA 35
CSI -.57

So, with the beginnings of scaling and two small calcium nodules what should my approach be? Borates are also low so can I bring them up with Boric Acid while I attempt to deal with scaling? This would raise pH obviously.

I look forward to recommendation. Thanks.


Gold Supporter
TFP Guide
Jul 21, 2013
Northern NJ
I don't think what you have is scale. Scale does not occur in isolated areas.

Calcium nodules and scaling are two different problems. @onBalance explains calcium nodules here...

As he says calcium nodules primarily form due to bonding failure (delamination) of a new coat of plaster, and occasionally from severe craze cracking, and that they were responsible for this plaster defect. Plasterers learned that bonding failure rarely occurs on fresh gunite substrates (new pools); however, bonding new plaster (replaster) to old plaster surfaces can occasionally be difficult to achieve. This is why most calcium nodules occur in replaster jobs.

Are those areas you identified as scaling rough to the touch like sandpaper?

Run your water chemistry on the low end of CSI between -0.3 and -0.6 for a few months and see if the aggressive water dissolves some of whatever it is. You always want to run your pool water CSI negative to prevent scaling.