Is it opaque white or translucent?
Is it blobbish or sheet-like or chalky or smearish?
Those sort of characteristics might help determine whether you have egg masses, plain old death-rot (from something buried in the sand), shedded mucus, or something else.
If I wanted to play it safe, I'd try to very carefully siphon a bit of the white 'slime' out, and sniff it for the stench of death. If it smells like a dead rat or a rotting fish --bingo, you may have to siphon most of it out to avoid a nutrient spike.
Keep in mind, lots of creatures can slough off mucus sheets and other coatings, and you may have something that benign on your hands.
Hope you can give a more detailed descrip, or better yet, a focused pic.
horge
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Cogum manent
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