sts solution will stay clear if u avoid contact with light, also during mixing it should not turn colour, this can ruin your mix. when sn reacts with soduim it turns dark and brown. thats why u need to mix slowly and not too much in one time, if the silver cant dissolve fast enough then it will react and this will not be a great mix.
sodium pentahydrate takes about 6 min to dissolve, nitrate dissolve fairly quick but the bigger cubes of sodium can take 6 min. just stir often and they will dissolve also.
when u add silver nitrate with sodium u should see a small white could that will dissappear when u mix at the same time, if u dont mix u can again get a bad reaction that it didnt mix fast enough. then u get nasty stuff in your mix and wont be clear.
the more distilled water u use the less effect u will see pooring silver nitrate in 500ml or 160ml will offcourse have less reaction. 500ml is a safer way to mix as there is more water content, while using less water u can see the reaction better so u know your stuff is working.