Ok cheers for the heads up guys.
Sadly my payment options are limited so will have to go with something online.
Citrofresh and either Canna Aktrivator or Pythoff sound like it will do the job?
Won't post a link to the site but it describes Pythoff as:
QUOTE
Pythoff is an advanced sterilising agent that eliminates harmful pathogens from all parts of your hydroponic system.
Pythoff has a unique formulation that dissolves into your nutrient solution and remains active as a sterilising agent for longer than many other alternative products.
This leads to a very high success rate in both preventing and treating pythium infections that could damage or even destroy your plants if left untreated. Do not use in conjunction with beneficial bacteria or fungi based products
It's a new one on me anyway but sounds like what I need.