By using the features on your filter's back wash valve, vacuum the D.E., after it has settled out, to waste. You may have to do this several times depending on the amount of D. E. you added. If you added no more than a cup or hand full ~ just vacuum as usual as this small amount may enhance the filtration.
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I have a pool company, we service several pools each week. One customer has a cartridge filter for an inground pool and there is always sand in it.
This customer has brick retaining walls around two sides of the pool. The more it rains or the customer uses the pool the more sand is washed into the pool.
I don't know if this applies to your pool.
If it is in-fact sand it has be coming from the environment around the pool.