I have been discussing my experiments with an Osmocote clone (Starxcote) in the following thread:
Root tabs and/or liquid ferts
Given the release pattern of Osmocote in water, it is better to insert a little bit weekly rather than all at once as this will smooth out the release curve (as shown in the diagram below Osmocote dumps more NH4-N in the first 2 weeks compared to other slow-release ferts like Nutricote)
I'm not sure how many Tropica Tabs you added and how many osmocote balls were in those Tabs, but I'm guessing it was probably too many at one go?
I also referred to the advice from 2hr aquarist. Do note that his recommendation is to insert after the aquasoil is exhausted, which implies this will be in a heavily planted tank with extensive root systems which presumably be able to use some of the NH4-N before it leaks out into the water column. But if it is in relatively new tank, then spreading out the insertion of Osmocote to smoothen the release curve seems ideal.
Fresh aquasoil such as ADA aquasoil contain high amounts of ammonia. This is very effective for plant growth, however, it does deplete over time. Spiking the substrate with root fertilizers such as osmocote is an easy way to enrich aquasoil with nutrients.
www.2hraquarist.com
p.s. you can add Seachem Prime as well.