[Cajundaddy]

The Pool and Spa biz was my game for 40 years. The Cliff's notes:

All EPA registered sanitizers will work effectively "if applied properly" and that last bit is where everything unravels. 99.9% of users do not test regularly, do not measure carefully when adding chems, do not drain and refill hot tubs often enough, do not keep hardness, TDS, phosphates, and pH in the recommended range. Then they are mortified that their spa water has an odor, feels uncomfortable, does not stay clear, clogs the filter quickly, destroys their heater. If you see yourself in this description, please forgive my frankness. So what to do?

Here are a few alternatives to choose from. I have used them all over the years and each has it's positives and negatives. There are no magic pills with 100% upside, sorry.

Bromine tabs (actually 60% Bromine, 30% chlorine)- Put them in a feeder and carefully test/adjust often to be certain they don't get too strong. Add 1TBS MPS shock after each spa use, keep bromine level 3-5ppm, pH 7.2-7.6, hardness below 200, TDS below 400, clean the filter often and drain every 3 months or if the spa water ever gets funky. Water is cheap.
Downside- Bromine does have an odor, different than chlorine but hard to miss. Most let bromine levels soar, pH levels to fall and the water gets uncomfortable, heater becomes corroded.

Frog (silver based sanitizer) + ozone generation: The combination does work "when applied properly". Keep pH 7.2-7.6, hardness below 200, TDS below 400, add 1TBS MPS after every spa use, clean the filter often, drain refill and change the Frog cartridge every 3 months.
Upside- If applied properly there is very little odor, the water stays nice, and corrosion is rarely a problem.
Downside- It is difficult to test for active silver ions and if you get this wrong, pseudomonas bacteria is a very uncomfortable outcome. It is at least 5x more expensive than chlorine treatment so our retail division loved it as a reliable profit center.

Salt system: This employs a disposable salt/chlorine generator which produces free chlorine at the anode and Sodium Hydroxide at the cathode by electrolysis when you charge the water with 1500ppm of salt. It sanitizes the water continuously and turns back into salt water. It sounds ingenious, works pretty well "when applied properly" and is the method I currently use. You still need to test regularly, keep chlorine levels 3-5ppm, pH 7.2-7.6, ** hardness needs to be around 50 to minimize scale in the cell, Salt level 1500-2000, TDS below 2500, drain and refill every 3 months and either descale or replace the disposable salt cell.

Upside- It can maintain a very well sanitized spa with little or no chlorine odor, a side benefit is the residual sodium hydroxide (found in many soap products) makes the skin feel artificially soft. Because of this effect, my wife thinks I am a God! I don't have the heart to tell her it is sodium hydroxide doing the magic.

Downside- It is the most expensive spa sanitizer system by far @ maybe 10x the cost of granular Cl2 but... Honey likes it and my retail division LOVED IT as a profit center. It does require special care and feeding, and a LOT of spa down must be added to keep the pH in range. I typically add 2oz per week.

If I were the only one using the spa what would I do? Use granular chlorine, "applied properly", keep my water carefully in balance, clean the filter often, change the water every 3 months.
Upside- Very low cost and effective, rarely any noticeable odor or skin irritation, simple enough to do well.
Downside- I would lose my Godlike status with women who just love that soft skin thing.

**Sorry kinda long, I boiled down my 2hr training class as much as possible. I hope it helps.