i assume its normal to loose 3ppm of chlorine is heater is on high?

It's also a function of your CYA level. If you have a lot of sun on the pool all day you might consider raising the CYA, especially to 50 ppm if you aren't there already. In very hot sunny climates such as the desert, people go even higher in CYA level (but not above 80 ppm since a SLAM becomes more difficult at that level).
 
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