Acid washing concrete to simply clean it, should never be done. The fact it was acid washed, the conrete's surface is damaged and it will always stain easily.
However, the steps below should help you.
If it's just yard dirt, usually a little TSP in water will usually clean concrete surfaces (Disolve 1 Cup TSP to 5 Gallons Water).
Use a Zim Grit pad with an industrial strength buffing machine.
Practice with the buffer away from the pool. When the buffer spins, it looks slow, but is powerful. An unexperienced user may end up with the machine in the pool.
Clean all of the concrete to be sealed in this way. Keep the concrete very wet while buffing. Then buff thoroughly with plain water while spraying off concrete and continually adding fresh water. When the water coming out from the spinning buffer stops looking cloudy, that's when the concrete is truly clean.
Wait about 24 hours before sealing. I suggest you use a durable professional IMPREGNATING sealer.
Impregnating sealers sink into the poors of the surface. Once cured, they are not slippery. I suggest using about four coats. Wait 12 hours between coats. These sealers don't get cloudy. They can be applied with a garden sprayer.
These sealers don't change the look or feel of the concrete once cured, but do protect concrete from staining.
Usually, the more expensive brands are usually better. Avoid impregnating sealers which are only for vertical surfaces they aren't as durable as the ones for horrizontal surfaces.
You should reapply a coat or two once a year.
Cleaning and properly sealing concrete is a very labor intensive process and is usually best left to a professional.