An acrylic tub is fiberglass in poolmath.
Its not really a long game persay - its a few hour game. Bacteria & other organics grow at an alarming rate in a hot, wet, dark environment. They form biofilms to protect themselves from chlorine. Bather waste contributes to this & only makes matters worse. The only way to get around keeping adequate amounts of sanitizer in the water all the time to prevent most of this bacteria stew
is to completely drain & refill after every use as you would a bath tub (this does not address person to person transmission of pathogens). Even bathtubs need to be sanitized regularly. Then there’s the jets (spaghetti of plumbing) that don’t get fully evacuated /flushed when draining.
Also in an outdoor pool there’s uv to help with the breakdown of cc’s - no such luck in a covered spa unless it comes w/ a uv system & those still take time to work.
The dichlor then bleach method for sanitation is simple.
Use dichlor to chlorinate until cya gets to around 25-30ppm (around 3 or 4 shocks) then switch to bleach/liquid chlorine.
Many people (myself included) use a swg to do the majority of the daily chlorinating. This allows you to only need to add bleach after a soak or heavy bather load. I use a little dichlor every couple of weeks to replenish my cya. I have had my spa for 3 years & am only on my 2nd container of dichlor.
The rest of the parameters have the same maintenance requirements as they would be with any other sanitation method to prevent premature wear/tear on equipment.
Spas have alot of aeration for the water volume- this affects ph rise much more quickly than a couple of returns in a 20k gal pool.
It requires regular monitoring & adjustment to prevent corrosion & scaling of spa equipment.
Adjusting ta to around 50-60ppm can help moderate ph rise & the need for frequent acid additions.
To add bleach/liquid chlorine or dichlor you need to open the cover , pour it in front of a running jet (avoiding the shell) & allow it to mix for several minutes before turning the jets off.
Leave the cover off for 15-30 min after adding fc/ soaking to allow any cc’s created to escape (this helps preventdegradation of your expensive cover).
A pool / spa is just like a pet - you need to feed it every day whether you play with it or not. My swg feeds my spa fc around the clock for me.
When you 1st begin you should test fc every day before & after use .
You will get a feel for how much fc your tub consumes daily when un- used & after regular use. Then you can just replenish the fc you know has been consumed.
Most people who manually dose raise to shock level for their cya
FC/CYA Levelsafter use & that’s usually enough fc to overcome the current bather waste & leave a residual amount that will be present by the next day.
Make no mistake- if you start out your soak with say 3ppm & it all gets consumed while you’re in the tub (maybe with other people) you have no protection from person to person transmission of pathogens. The goal is to prevent this from occurring. The only way to get a feel for your tub’s consumption is to test the water with an fas/dpd test.
Your original post stated that you had to drain & refill often & implied that you were unhappy with doing so.
What i have described (& what’s in the guide) is the path to keeping a small body of water sanitary for 4-6 months.
I do highly suspect you’re gonna need a drain/refill moving forward but let’s see what somebody more knowledgeable than I says. I also suspect a flush with Ahh-Some cleaner maybe in your future as I’m wondering if there’s some nasties built up in your pipes.
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