carbonate hardness <kh> and phosphate <po4>

[i have crabs]

since your calcium is on the lower to mid end and the alk is a on the upper end so i would add some calcium to raise it up to the 450 or even 475 range
thier can be a lot of reasons for phosphates feeding is just a common one,do you have a sand bed? and maybe check how dirty your filters are depending what you use