Congrats! I didn't even realise you were a Kiwi till i read the references to Mac's and Steinies!
Agree with your leasons learnt about the star san, got a bottle of it and after a few batches I am still above the 8 oz level of the 8 oz bottle!
The weird issue with you hydrometer could be from the temperature of the sample, the hydrometer is calibrated at 16 (or 21 - should be on it) deg C and the reading will be slightly higher or lower if the sample temperature is different.
ANd don't worry about if the temp is around 18 deg C, thats a better thing for your beer than being at 24 deg C. Have a read round here and you will see most of these guys recommend fermenting in the 60s (deg F - damn USA not getting with the times

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Also I think I spotted the 2 links between your old blog and new one - bottle cap and Bin Inn (did you get the brewcraft starter set?).