At this point your Aquarium Soil may be relatively depleted - obviously this will depend on plant growth, water parameters, regular fertilizers use etc
Carpet plants definitely get “tired” as substrate ages (Green Aqua, Jurijs, Filipe Oliveira all mention this)
ADA also warns that Amazonia allowed to dry out is more likely to collapse and “mud”
If you decide to reuse your old soil, I’d definitely use bottom additives
- such as Tropica Nutrition Capsules: watch Jurijs mit JS
Aquascaping Masterclass video for details - I don’t recall his recommended dose - scatter some (new soil), then opened capsules etc)
- ADA system of tourmaline etc (I used Power Sand once
it kept resurfacing and drove me mad as it was all I saw every time I looked at the tank
)
- you could also add a layer of Tropica Growth Substrate (1-2 cm) but if you like to adjust your scape frequently or occasionally - this will mud the water column so be ready with water changes, extra Prime etc
Even with the enriched bottom layer, I’d still mix in some new Amazonia (or whatever) ... maybe up to 30% new soil depending ...
I just replaced the aquarium soil in my 90cm & 60 cm tanks
I’d set up a new 60P with Tropica soil and the difference in plant root growth & leaf growth was significant, so decided I’d switch out my other tanks on the next rescapes (I like to change plants in running scapes, or even change hardscape etc)
Note I have very soft tap water with minimal nutrients so this definitely impacts substrate longevity
Of course I remembered that I meant to add Tropica Nutrition Capsules to the base layer once I’d gotten well into the planting stage
... next time I just might remember in a more timely fashion