Changing to sand isn't that hard
I didnt remove any of my fish for the change over, i prewashed the argos sand over and over so the water runs clear,best to do this a bit at a time,i put sand in a bucket around quarter full,then just keep churning it over,tipping the water out and replacing...the cleaner you get the sand the better it will be in your tank with no cloudiness.
Anyhows i removed decor from half the tank, then using a wide hose (from the gravel vac) sucked out the gravel into a bucket,you could scoop it out,but its surprising how much gunk traps in gravel...
Then i put some sand into a jug,carefully lowered the jug into the water,if you let the water go carefully into the jug, you can lower it to the bottom of the tank,then pour it out slowly, this way has long as your sand is clean you will get little bloom if any.
Then do the other half of the tank the same, put the decor, plants back in, my fish stayed up one end whilst i worked at the other
I used nearly 2 bags of argos sand in my 55 gals, so in theory i would've thought a bag would be enough for yours,you could always get a spare bag for future top ups
Just remember to turn off your filter whilst you do it, has long has you've washed well,you can put the filter straight back on after.