Sorry to be posting so much!!!
Are these any good and which would be best?
http/cgi.ebay.co.uk/D-D-TDS-Meter-Hold-Digi-Thermometer-WATER-PURITY-/320678003366?pt=UK_Pet_Supplies_Fish&hash=item4aa9e602a6
I know this is marine chit chat but when I was using RO water for my tropical setup I bought one of the ones in the first link as it was recommended by a couple of the lads at my local MA. Only used the meter about half a dozen times because I changed over to Tanganyikans but I found it to be a good bit of kit, so if you`re interested in buying it for a bit cheaper than the ebay ones give me a shout