It needs to be cleaned and there's no way I'm letting my dc bath in there without cleaning. We are staying for part of half term In the house and I'm going to have to clean it. The shower curtain and bath mat have an orange tinge, I'm guessing it's some sort of bacteria? I asked when the bath was last cleaned and he said 6 months ago 
All round the sealant looks damp and blackish in places.
What do I clean it with?