Al,This is a truly perplexing problem, and I can understand your frustration. You've done a remarkable job of documenting and investigating the issue, and the fact that you've eliminated so many potential causes makes it even more baffling.Let's break down what we know and explore some less common possibilities

Summary of Findings:
Scale Composition

Calcite (Calcium Carbonate)

Scaling Location

Primarily on the ADA lift (316 SS) and pool light ring (304 SS), but also affecting a brass fitting.

Scaling Rate

Extremely rapid; within 24 hours of reinstalling the lift after cleaning.

Water Chemistry

You are diligently managing pH and calcium hardness, although pH tends to drift high. Pool service company confirms acceptable levels. Conversion from salt to chlorine did not solve the problem.

SS Grades Verified

The lift cylinder material is confirmed to be 316 SS.

Control Experiment

316 SS and 304 SS samples immersed in the pool water show no scaling. This is a critical piece of evidence.

Stray Current Investigation

Voltage measurements appear to rule out stray electrical currents as a primary cause.

Timeline

Scaling began shortly after pool renovation and lift installation.

Unusual Acid Demand

You are using a high volume of muriatic acid to maintain pH.

Possible Causes and Considerations (Beyond the Obvious)

Given that you've ruled out many common causes, we need to consider factors specific to the lift and its environment.1.

Electrolytic Reaction (Even Without Stray Current)



Dissimilar Metals Proximity

You mentioned the brass fitting at the base of the lift. Even though you've tested for voltage, the presence of a dissimilar metal (brass) in close proximity to the 316 SS in an electrolytic environment (the pool water) could be setting up a localized galvanic corrosion cell, even without external stray current. This might accelerate calcium carbonate deposition on the 316 SS near the brass.

Mitigation

Thoroughly electrically isolate the brass fitting from the stainless steel. Use non-conductive fittings or a dielectric union. Consider replacing the brass fitting with a 316 SS fitting. You could apply a protective coating to the stainless steel cylinder that is compatible with submersion in chlorinated/salt water. The coating must be compatible with stainless steel and not react adversely with the pool chemistry.2.

Surface Condition of the Lift Cylinder



Passivation Layer

Stainless steel relies on a passive chromium oxide layer for corrosion resistance. If this layer is damaged or incomplete specifically on the lift cylinder, it could make the surface more susceptible to scale formation. The process of manufacturing the lift could have contaminated the surface.

Surface Roughness/Microscopic Imperfections

The cylinder's surface might have microscopic imperfections or roughness that create nucleation sites for calcium carbonate crystallization. The smoother, polished surfaces of your test pieces might not offer these nucleation points.

Remedies

Passivate the lift cylinder thoroughly with a citric acid passivation solution specifically designed for stainless steel. This will help restore and strengthen the passive layer. Make sure the product is safe for your pool environment. Follow manufacturer's instructions carefully. Consider lightly polishing the cylinder to reduce surface roughness. Be extremely careful not to damage the base metal during polishing.3.

Localized pH Variations Near the Cylinder



Micro-Environment

Even though your overall pool pH is managed, there could be localized pH spikes or alkalinity gradients right at the surface of the lift cylinder. This could be influenced by water circulation patterns or the surface chemistry of the 316 SS itself. Calcium carbonate precipitates more readily at higher pH.

Buffer Capacity

Consider the buffer capacity of your pool water. Is it possible that even small localized changes in pH near the cylinder surface could lead to scaling, even if the bulk water chemistry appears stable?

Testing

Attempt to measure the pH immediately adjacent to the cylinder surface. This may require specialized microelectrodes or pH paper carefully applied to the wet surface.4.

Water Circulation Patterns



Dead Zones

Is it possible that the area around the lift cylinder has poor water circulation, leading to a build-up of calcium and alkalinity?

Test

Check the circulation in the area of the cylinder and around the pool. You can use dye to confirm.5.

Specific Chemical Reactions with the 316 SS Cylinder



Manufacturing Residue

The manufacturing process for the lift cylinder might have left a residue on the surface that promotes calcium carbonate deposition. It is extremely important to eliminate this possibility since the purchased 316 SS did NOT scale up when installed.

Water Quality Issues

Look at the source of the pool water. Is it possible there are unusual trace elements or organic compounds in the water that are interacting with the 316 SS specifically to promote scaling?

Testing

Have the pool water analyzed for trace elements (phosphates, silicates, iron, manganese, etc.) and organic compounds.6.

Material Defect in the Cylinder



Manufacturing Defect

There might be a defect in the 316 SS of the cylinder (e.g., inclusions, compositional variations) that makes it more susceptible to scaling than the samples you tested. This is less likely, but possible.

Testing

This would require destructive testing of the cylinder, which is probably not feasible.7.

Check Your Acid Source



Contamination

Even muriatic acid, which is typically relatively pure, can sometimes be contaminated with trace elements that could contribute to scaling.

Try a Different Brand

Try using a different brand of muriatic acid from a different supplier. This is an easy way to rule out acid contamination as a factor.

Action Plan


Isolate the Brass Fitting

This is the first and simplest step. Replace it with a 316 SS fitting, or thoroughly electrically isolate it from the stainless steel of the lift.2.

Passivate the Lift Cylinder

Thoroughly passivate the entire cylinder with a citric acid-based passivation solution. Follow the manufacturer's instructions precisely.3.

Inspect and (Carefully) Polish the Cylinder

Examine the cylinder surface for any visible imperfections. If possible, carefully polish the surface to reduce roughness. Be very careful to not damage the surface in doing so.4.

Localized pH Measurement

Attempt to measure the pH directly adjacent to the cylinder surface.5.

Comprehensive Water Analysis

Have the pool water tested for a wide range of trace elements and organic compounds.6.

Test Alternate Acid Source

Try a different brand and source of muriatic acid.7.

Circulation Test

Perform the circulation test as mentioned above to see if there is a "dead spot" where the lift is located.8.

Consult a Metallurgical Expert/Corrosion Specialist

This is a complex problem, and it might be worth consulting a metallurgical expert or corrosion specialist who can analyze the situation in person.I know this is a lot to consider, but given the unusual nature of the problem, a systematic approach is necessary. The fact that your control samples didn't scale is the key clue. That means something specific to the lift cylinder itself, or its immediate environment, is driving the scaling.Good luck, and please keep me updated on your progress. I'm very interested to see how this resolves.

Disclaimer: I am an AI chatbot and cannot provide professional engineering or metallurgical advice. The suggestions above are based on my knowledge and understanding of the situation, but you should consult with qualified professionals for specific recommendations.* Flag for review