Wonkhester: Waterbear has made numerous postings for you to follow. Just do what the man says and you will see vast improvement. Regarding the hot tub rash, I am somewhat informed what causes this in many cases and would instruct you again to do what Waterbear says to do. Besides following his chemical recommendations it is extremely important that you Purge your hot tub with a high-quality purge product. The recommended purge product is the AhhSome as it will remove the bacteria that is most likely causing your rash. That bacteria is Pseudomonas Aeruginosa. The Ahh-Some product has been tested at America's #1 Biofilm Testing University, Montana State University, and is successful in removing this biofilm. Actually, when compared to an enzymatic purge product the ahhSome was rated as being more effective at removing the "PA" biofilm by over 5,000%. This data is on the internet. You mention a product in one of your postings called Spa Marvel. This may be a worthwhile product but I recently found information on this enzyme that was put to the test by an "OCD" hot tub owner. I will attach the link here for you to read since you previously brought this product up in your recent post. What this forum tries to do is help you. I have been more active with my postings of late because I see so much mis-information and speak to hundreds upon hundreds of hot tub owners who are frustrated because they hear so many methods and recommendations. This forum and its participants really have your interest at heart. So Wonkhester, follow what Waterbear has told you. His wisdom on the subject of water maintenance is enlightening. Here is the article I ran across on the Spa Marvel.
https://rvdoug.com/blog/spa-marvel-review-part-1-the-enzymes/