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Coincidence? Maybe. Never pour straight muratic acid in a hot tub. Always dilute it with water no less than 20-1. A 5 gallon bucket with 1 cup of acid mixed well.
I suspect much of the damage is done, have you checked the pH of the water in the tub since you did this?
I suspect you have done considerable damage to all your pumps, pump seals, and the interior of your heater, perhaps also the plumbing fittings on the jets and maybe the finish on your tub. This of course depends on how much was a "generous amount", a pH test now will tell you if your water is still acidic and still eating away at things. This is sort of like tossing some gasoline and a match inside your car to get rid of an odor problem.
Do you have test strips to check your water balance? if so....like Isaac-1 has said...check the PH level...If its way low you can drain a portion of the water out and add fresh water to dilute the ratio and bring the PH up or add PH up to the existing water to balance...it mainly depends on how far off balance you are...I personally prefer to drain some water and refill to use less chemicals.. Was your tub totally empty when you added the acid to the grey tube??? (24 hour recirc filter tube) or was the water just low enough so you could get the acid in the tube? I would agree that you didn't do yourself or your tub any favors by doing this but lets stay positive and hope that everything is going to survive...Here's what your probably looking at..If there was some water in the tub when you added the acid I would think you will have a better chance of surviving this learning experience! Chemicals can do serious damage to a spas interior and components and even tho we don't see it...the damage is there. Essentially shortening the life expectancy of the components and damaging the appearance of the tubs shell and jets, tubing, plumbing, heater, etc...But test the water ASAP and get the PH under control because if the PH is too low you are still doing damage!
Don't panic you will be OK Your dilution ratio was fine you are right but it is the initial spot you poured it in that will suffer. You said you poured it in the filter right? Check the filter for damage and if there is any it will be in that line feeding the circ pump and the heater. After that it will be so diluted it will be fine but checking your PH would of been the thing to do after that. Acid will drive down PH which means acidic water. And if your PH was OK after no biggy. Just don't make a habit of pouring acid down into your filter and lines.
And get yourself a way to check your PH accurately.