Something to look out for, I thought I would mention my experience of doing an in-pool acid wash (CSIs of between -0.40 to -1.00 are I believe used for in-pool acid washing), I have noticed my cell seemed to be less efficient than normal after the first day. The next day I removed it for inspection, sure enough there were deposits on both ends, so I acid washed it in 4 parts water and 1 part muriatic acid. But I only gave it about 5 minutes total.
Four hours later I, by pure good fortune, read the manual and it stated soak it for up to 20 minutes. This I intended to do the next morning, had I soaked it for 20 minutes the first time I might never have found this issue.
I removed it again the next morning and to my surprise I found nearly as much deposit as at the start of the previous day, but more sludge like. I soaked it for 15 minutes. The pool does not seem to have much scale on it but maybe there is more than I can see. The surface of the pool's plaster is white and not colored therefore it might be more difficult to know.
The cell is a Pool Pilot SC-60, the cell is mounted vertically, and has a pressure relieve valve below it, water passes more slowly over the cell and this may be the cause (lower pressure). Cells where the pressure is not lowered such as my neighbour's Aquapure 1400 may not encounter this issue. Now that I am aware of this I will check the cell each night and shoot it out with water if any further deposits appear, possibly acid washing the cell again (I hope not), until done with the in-pool treatment.
I have been very happy with the Pool Pilot system over the 2+ years I have had it, I give it a full service weekly, I would buy it again and recommend it if you want an acid feed system. The only issue I have had, now finally resolved, is the cable to the Tri-sensor will not work properly if it is not given a full flat run, winding it up in a circle causes the unit to malfunction, large curving bends are ok.
Added after posting: The pool is vacummed continously by a Great White wall side suction vac with a Hayward leaf trap in-line into which I very recently inserted in a cheapo pool sock which captures more pollen and tiny seeds than the mesh, both are in there just in case the sock gets loose and gets sucked into the pump, aahh. Not sure of it's mm capture ability but obviously lets this fine sludge through. Main drain is turned off and skimmer is only opened a tiny bit.
In the"Dealing with scaling/stain during pool season" post geekgranny mentions a sludge sock, do not know if that would help, maybe I could insert that in leaf trap. Any thoughts? It might be easier than taking the cell off daily, and then might be useful later for filtering iron in solution, yes or no? I did notice the sock is getting browner and browner daily even though I wash it out, presumably iron although I have not tested it with a vitamin C tablet.
The pool itself is looking better than it has in years (15 year old plaster pool -looked after improperly the first 5 years) and see virtually no iron deposits, now after 10 days, the magic pH number seems to be 7.3, even at 7.4 which I thought was the magic number very, very faint traces of iron seem to show up, so I turned it back down to 7.2 to do the in-pool acid wash. In the future I will run it at 7.3, and balance accordingly. I do now use Jack's Magic "The Purple Stuff", the first stuff in years that really seems to work, only available in Hawaii this last month. My daughters bought me Jack's test kit, through Amazon, but they will not ship it to Hawaii, a friend is tran shipping from New York City, who the heck can afford a pool in NYC?
Hope this helps and if anyone can advise me on the sludge sock idea to remove iron that would be great, as it is not cheap, for a sock that is.