Chlorine (Fc) Drops To 0 Over Night?

[spanoob9]

I'm new to water maintenance, I just recently filled my 500 gallon spa. I'm sanitizing using chlorine (dichlor). After filling i raised fc to 10 ppm, it dropped to 1-3 over night but that was after leaving the cover off all day and about 45 min of use.

Now i've been checking the fc every day and its always close to 0 (~1 ppm). i add about an ounce of chlor-aid, and it raises to about 5 ppm fc. Yesterday after raising to 5 ppm, i left the cover on all day, no usage, checked the water again this morning and it was again near 0. Is this normal? Should i keep adding an ounce of chlor-aid everyday? I also have an ozone injector installed. The water is very clear looking perfectly clean, just hoping to keep it that way.

[chem geek]

Is the Chlor-Aid you are using this stuff? If so, that's Dichlor. Is this a new spa? If so, then you may have biofilms or grease in the pipes. For a new spa you would normal use SeaKlear Spa System Flush or Ahh-Some. You only need to use that once; thereafter you maintain a proper chlorine level. At this point, you may also need to decontaminate by raising the chlorine to a high level and then changing the water.

[spanoob9]

Its not new, 4 yeas old.

Thing is the water is crystal clear. No oder, no bubbles, no oil/chemical deposits. I just filled it also

I talked to a professional today she said it may be bad phosphate levels or non-living organic build up in the pipes?

[chem geek]

You said you were new to water maintenance, so is this spa new to you (i.e. you got it used) and this is the first time you've used it? If so, then that is like a new spa in the sense that the chlorine levels went to zero and you don't know if the spa was properly maintained in the past. If that is the case, then my recommendations about spa flush still apply.

If the chlorine got to 0 for more than 12 hours, then you could have biofilms which create a large chlorine demand. As for the phosphate levels, that would only be an issue if your chlorine level got low and the cover was off since then algae could grow (with the cover on, I presume it's completely dark in the spa). You can shock the water with chlorine if it's algae growth, but if it's biofilms you'd have to either superchlorinate or use one of the spa flush products I indicated.

[spanoob9]

I've taken over maitnence of the spa from my dad. There was a period of about 2 months where the spa was left untreated. At some point the circ pump died...

So I replaced the pump, drained it, refilled it. Could there still be biofilms even after I refilled it after the long period of no treatment?

[chem geek]

Yes, that is still possible, though depends on humidity. Water can last in the plumbing for weeks certainly due to the lack of air circulation. I just wouldn't chance it and go ahead and do the decontamination or spa flush.