I concur. Just to explain a bit about fertilizers...
As you are in the UK, you could use Total Nutrition's compr4ehensive liquid fertilizer. They have two, one is called TNC Complete, the other is TNC Lite. The Complete has nitrogen (as nitrate) and phosphates, whereas the Lite does not; all other nutrients (so far as I can remember) are the same in both products. Here, with no fish, the Complete might be preferable, but once you have fish, use the Lite. With fish in the tank, nitrogen and phosphates will never be lacking and will be sufficient for the plants.
Another good product is Seachem's Flourish Comprehensive Supplement for the Planted Aquarium. This has all nutrients (except oxygen, hydrogen and carbon) that the plants require, including (minimally) nitrogen as ammonium and nitrate. The Flourish Tabs are one of the best substrate tab fertilizers there is. For the liquid, another good one is Brightwell Aquatics' FlorinMulti.
The above products are complete, or comprehensive, and intend as "supplements," so they work extraordinarily well in natural or low-tech method planted tanks, which is what you are dealing with here.