We have had a small (~800L) spa for around a month. Ive begun using the dichlor-then-bleach method today after half-draining the spa to reduce the CYA to close to recommended levels.
1) How often? The providers said drain every 3 months, but apparently that's too long for a small spa. The Taylor site recommends the formula:
Size in Litres / (10 x # of bathers daily) which comes to just 40 days for us.
I think we should be able to go longer than that, because we wash with soap first and we are pretty small people. What guidelines do other follow? I'm thinking 2 months.
Is there a more scientific way to say when to drain (provided of course the water looks fine and sanitised correctly each day)? Perhaps a total dissolved solids measurement?
2) Draining onto garden? Im using the recommended 50 ppm borates, and I understand that a little is good for plants, but that is going to be a lot of borates over time in the soil.
What do others do with the drained water?