By The Zagosa Team. Published .
Reviewed or updated .
A refill is a clean slate. Done in the right order it needs roughly 24 hours of background time and maybe half an hour of hands-on work. Done in the wrong order it can drag on for a week and swallow twice the chemicals.
Hour 0: fill and fire up the heater
Fill to the marked line through the filter housing rather than the open shell. Put the cover on and start the heater.
While it warms, test the fresh water for hardness and alkalinity. These are your baselines. Know what the fill water gives you before you change anything.
Do not add chemicals yet. Cold water dissolves things poorly and you risk staining the floor of the tub.
Hour 6 to 12: warming up, sequence the chemistry
Once the water passes 25C, add alkalinity increaser if needed to reach 80 to 120 ppm total alkalinity. Wait an hour and retest.
Then look at pH. With alkalinity in band it is usually happy in the 7.4 to 7.8 range and may need nothing. If it is too high, dose pH down sparingly and give it an hour.
Next, calcium hardness. Bring it to 100 to 250 ppm with calcium chloride flakes dissolved in a bucket, added slowly with the jets running.
Hour 18 to 24: sanitiser and a final shock
Once the tub reaches 38C, add sanitiser. For chlorine, dose to 5 ppm with granular dichlor. For bromine, load a fresh feeder and add 30g of sodium bromide to seed the bromide reservoir.
Leave it an hour with the jets on, then test free chlorine or bromine and adjust if needed.
Finally, add a non-chlorine shock. Run the jets for 15 minutes with the cover off, then cover it and leave it be.
Next morning, retest everything. Every reading should be in band and the tub ready to use.
FAQ
Why not dose it all at the start?
Cold water dissolves granules badly and the readings will not settle until everything has integrated. The phased method takes longer on the clock but uses less product and gives a far steadier result.
Can I drop the final shock?
Yes, if the rest of the routine has gone well. The shock is belt and braces, oxidising any organic matter the new water picked up from the hose, the filter or the air. We always include it.