Hi
My apologies for not replying for months, things have been very hectic!
I have discovered what the TDS issue is, and I feel pretty stupid TBH, I watched YouTube video which suggested minimal gravel cleaning was best for planted tanks. I have always done deep gravel cleaning in the past, and switched back to that a couple of weeks ago and Hey presto the TDS is dropping! See attached weekley record of tank parms. I tested today and it was 1040, so I have definitely found the problem!
Substrate is aqua one black gravel.
Regards
Steve