s310t, new sand

after 9 years a neglected system wasn't filtering correctly, has never had a sand change and im replacing the multiport which has cracked and the lateral assembly which was also deteriorated where the up-tube connects to the multiport.
after a bit of looking around im going to use HTH brand sand
So in vacuuming the sand out i started to think it might not have been the correct sand( perhaps play sand) installed when the unit was first placed( i honestly don't recall if it was me or not).
This is mid/low layer sand http://i.imgur.com/XS8JC4U.jpg


Also, i noticed when vacuuming out the old sand it seems the sand got progressively more compacted the closer i got to the laterals, sand was very fine and though it was wet seem compacted really badly.
Ive re bedded resin in water softeners and some units use/require a gravel bed at the bottom, i wondered if adding a layer of course, smooth gravel to the bottom to cover the lateral would help or hinder the back wash.

Sand will never wear out, it is the same today as the day it was put in your filter. With good pool care, you shouldn't need to replace it. In fact, sand filters work better as they trap particulates that "fill in" the spaces between grains, so they can filter smaller particles than fresh clean sand (unless you pump is too big, pushing everything through). That is probably why your sand was more compact as you dug deeper, which may be a good thing.

That being said, if you are having trouble with filtration and you don't kow where your sand came from, I would replace it. I have heard of putting gravel on the bottom, but I am not sure that would help. Sand would just work its way in between the rocks and around the laterals anyway. I think some manufacturers may say to do this, would check with your filter's manufacturer. Maybe someone else has more info on this.

Now you should follow the manufacturers advice or risk any warranty issues, Blah blah blah. Without any information on your system in your signature advice is tricky, some suppliers do say gravel over the laterals as it does help to diffuse the backwash but from my experience most filters backwash isn't all that good leaving plenty of dirt remaining behind in areas where the water doesn't reach. The Hayward S310t seems to be just sand and not gravel.

Sand is in use in lots of filters around the world but I am not using it any more as there are better alternatives, yest it's really cheap but it can be bettered but there isn't much point in fitting anything else unless you have the correct flow for the size of your filter and that is probably slower than what you have now as slower filtration is better filtration. The pool industry generally feels that faster is better but that's up to them and of course up to you.