Well, we cannot tell from just one number.
We need to full set:
FC
CC (or TC)
pH
T/A
CYA (stabilizer levels)
Also, don't sample the water from the skimmer, sample it from a fairly innocuous part of the pool.
AS A W.A.G. (Wild "Absurd" Guess) I'd guess your CYA is 0 and you have something growing and it's "eating" your chlorine down after you add it.
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