My experience, and what I hear from others, GFCI's are not very useful for submersible pumps in hydroponic greenhouses. There are just too many nuisance trips. I think that it is difficult to have the pump motors truly impervious to water intrusion. On the other hand, being in the salt water environment from the nutrient solution. The usual solution is to make sure that the pumps are well grounded. Nevertheless, I sure would like the security of GFCI protection.
I have been able to get in-line GFCI extension cords. Are similar devices available with adjustable trip current settings?
Bill