I would like to add, that when dosing liquid fertilizer to the
planted aquarium, one should start with very small doses, and
gradually build the level to 1mg/l.  Calculating what it would
take to bring it to the proper level and then adding it all at
once can create a problem or two.

Cryptocoynes do not like drastic changes of any sort, and since
addition of fertilizer would qualify, they could go into melt-down.
Vallisneria is also prone to turning red and/or dropping leaves
in this situation.  I'm certain that many other plants may react
in a negative fashion to slug-dosing, but these two are more apt
to do so, at least in that they do so, rapidly.

I think it's best to test the water, determine what is needed and
slowly over a period of days, bring it up to the proper level.
This should insure that the established growth is not set back.

There are exceptions to this, in that when using a wet/dry filter
with a large capacity sump, more liquid fertilizer may be added simply
because it is diluted before it reaches the plants. Otherwise it is
best to light on the liquid and gradually build it up.

When doing water changes, test your water and match the present
level of fertilizer, and add small doses daily afterward.

I'm sure there are those who will say that it has never damaged
any of their plants by slug-dosing.  In this case it just could
be that they are not over-dosing at all.