Soft Grout

[Fran]

I have recently bought a property and have drained the 7 year old pool, (long story why, but not really relevant to my point) and find that the grout between the mosaic tiles is very soft and can be removed with a nail or scrubbing brush.

I don't know whether this is likely to be an issue of using the wrong product initially, filling it before the product was cured or poor control of PH and/or CH (or something else).

My questions is: will this harden if left to dry fully, or do I have to rake out and regrout, or is there another solution?

Many thanks in advance

[Teapot]

It is a tricky one to answer as pool grout shouldn't become soft, so is it faulty? No real way of knowing unless you can find out who made the grout and ask them.
If you re start your pool with a high TA bicarb solution this will form a hard, tough calcium hydroxide layer and may cure it over a couple of weeks but cannot be certain.
If you do end up re grouting, use an epoxy based pool grout, a bit mork work to apply but much better long term result.