Slow watermelon growth

[chancethegardener]

I am growing Ali Baba watermelon along with Charentais and a casaba melon this year. They are all in the same bed and the growth for all of them is very slow. What might cause this? Soil in the bed has lots of compost, and I mixed crab shells/lots of brown leaves end of last fall. 2 months ago I added lots of Tomato-tone (since this is a relatively cheaper option in terms of fertilizer). Also temperatures have been very good and soil has good drainage.
One note: I have one Ali Baba plant in a pot and that pot also has crab shells + Tomato-tone in it. This plant is growing a lot faster than the Ali Baba in the raised bed.

[saltmarsh]

Could be the cloudy weather and cooler nighttime temps you're having. Do they get full sun? You might ask the melons if they like being in bed with a bunch of crabs. Try playing a few K. D. Lang songs for them. Claud

[dice]

Compare the leaf color on the one that is growing faster and those
that are growing more slowly. Are they a lighter green? If so, maybe
they need a little nitrogen boost (a gallon of diluted fish emulsion
per plant will do that; give it a couple of weeks before looking for
results).

[chancethegardener]

lol salmarsh, I'm afraid that crabs will come alive, and yes watermelons get full sun.
dice, leaf color seems to be ok (and there is a lot of fertilizer in the bed). I will take your advise and water with Neptune's Harvest. Do you think nematodes could be the problem here?

[dice]

I have never gardened down there, so I am not familiar with local
nematode problems. Here is a write-up on it from UFL, though:
http://edis.ifas.ufl.edu/ng032