Thanks again - I think we're going to go with the Seachem.
When I use the Seachem, will ammonia readings still show up on my testing kit?
Also - will I need to keep using it forever once I start (at the moment I don't care if I do - but thought I should check).
Ammonia readings shouldn't show up but if they do you'll need to water change again and add more Seachem Prime. I've found it magic stuff though.
Once the tank has settled you can swap back to another conditioner if you want tho Seachem works out cheaper. I use 0.25ml per 10 litres.