so you're also growing avocado?
I grow this inside so they don't get earthworms in the post since we bought soil for indoor planting
Are you Dutch cause they call earthworms "regenworm" here meaning rain worms :)
I normally replace the soil when its warm enough, its too early to do that now but perhaps I could try .. am worried to do anything at all and risk killing it
I did a few years back. I had one, which I grew from a seed above the water being held by toothpicks. Ups. I forgot to check it for translation. I'm from Slovenia, and here they are called "dezevniki", which literally means rainworms. Thanks for translating it correctly instead of me.
I also grew it inside, but I used outdoor soil and not the bought one. So I agree, this can't be the reason for your avocado to be sick.
I started growing avocados from a pit above water as well! I started planting them straight into a pot a while later and now I'm planting them straight into the ground! These seeds have a particular trick than involves "finding two halfs for each one and leaving a sort of not buried more than half of the bottom of the avocado pit and not leaving the top half too much above the soil".
I always get to see the seedling growth and I know by its "greeness" and different vibrant colors how well is doing so.
Look how some leaves are also having a similar problem to yours. Some sort of "underdevelopment". But also take a moment to watch how beautiful their colours are!