The only way to do it is the pantyhose method. Get new pantyhose or a mesh bag designed for aquarium filter media, rinse well. Suggested amounts of gravel is 1 lb to 1 gallon or more - probably more like 1.5 lbs to 1 gallon for a planted aquarium. if I were in your place, I'd remove 1/2 of the old gravel, and replace with 1/2 quantity of the new gravel in a mesh bag, let that sit in the tank for 2 weeks, remove all the old gravel 2 weeks later, and add the rest; rinse the new gravel really well and then rinse it in dechlorinated water and let it sit for a few minutes. Make sure when you remove the last of the old gravel and add the last of the new that you put the stuff that HAS NOT been sitting in the tank on the bottum and the gravel that has been in the tank for 2 weeks in a layer on the top.
What kind of filter do you have? With a mechanical filter you'd be in luck because most of the good bacteria will live there, so in that case this is just a "better safe then sorry" measure.
I would also suggest an extra 25% water change during this time.
Let me know if you have any questions
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