A) No need to be rude...
B) Ok 'recipe for disaster' was a bit dramatic but using aquasoil with gold fish is just not a great choice. It will result in debris in the water because they will break it down in their mouths as they turn it over constantly and debris will get into the water column and make the water look dirty/cloudy. You even say it will end up on the water column in your post which is not normally the objective. The majority of people want as clear water as possible for the least amount of effort possible.
Lets not forget its £30-£40 for 9L which is incredibly expensive and the person is looking to buy a budget friendly all on one tank. There is also very few plants that goldfish will not just straight up eat and most of those that are widely available ones do not benefit from aquasoil. If you really wanted a planted goldfish tank something like Eco-complete or Seachem Flourite would be a much better choice.
I wasn't being rude, i like tanks to look good thats all, i think it keeps the keeper more intrested if you do a tank more natural imo.
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