OK - I'm an idiot.
Should have read - http://tftestkits.net/Test-Kit-Instructions-10.html rather than the instructions in the lid of the Taylor K2006 kit...
Backstory here - new-pool-owner-and-new-pool-newcastle-australia-t72200.html
Was battling a mustard algae problem, lots of chemicals added (tons of bleach, copper algaecides etc).
I've been testing with a Taylor K2006, using a 10ml sample, and err... 2 scoops of R-0870 (aagh!) as the FC has been pretty high - I read on the TFTestkit website the instructions are to use one scoop. Dang. No idea what that would have done to the results (falsely double them?).
I've also been having very high PH readings, which I have been adding muriatic acid, with the end result of a TA of just 30.
(Since read that PH readings are inaccurate at high chlorine levels)
So I used the poolmath calculator to fix the TA problem - 30 to 80 (5m long, 3.5m wide pool with a 1.52 average depth = 32,300 Litres) and it stated about 3Kg of buffer - I put in 2Kg, and ended up with 100ppm (??!) which isn't ideal for a SWG pool.
Even weirder was the fact that the 45ppm CYA tested a few weeks ago now appears to be less than 30 (ie. could still see the black dot on the base when all the solution was added) - so added 1.5Kg cya - will test tonight.
PH tested at about 7.8 this morning, with FC at 17 (or 8.5 - not sure now).
I'll retest the chlorine tonight, and figure out whats going on here. A bit more acid should drop the TA.
Salt levels are also too high so I will probably drop some water out as well there.
Pool looks perfectly clear now, but getting this chemistry right... Hmmm.
CH is only 100 - is this an issue with a fibreglass pool? Seems pointless to increase it at the risk of scaling and having to remove deposits from the SWG cell.