"When it rains...it POURS!" - That's my motto for gardening pests :)

After what seems like hours of research regarding spider mites, I've established a VERY strict spraying regime for my outdoor potted citrus trees. But it seems as if more of the mites have moved in! I don't find them on the underside of leaves, but rather in huge masses in the potting soil itself :(

The little buggers don't seem to die! I've tried drowning them by flooding the pots, but I haven't noticed any improvement.

I'm contemplating repotting the trees in new soil to give them a fighting chance. What this be too extreme? They are between 2-4 years old, so not very large.

I've also found larvae in the first few inches of soil. I believe it is from flies that are attracted when I fertilize with fish emulsion. Is this something to worry about?

Any advice would be greatly appreciated!

-Kathleen