I used to use powder-Persil non bio powder,but noticed on the dark clothes that powder substance was being left behind.I had a free sample of persil non bio liquid capsules sent thru the door,used them and have done ever since.They are the round blue liquid capsules.
You're supposed to use 2 per wash,but i only use 1 for darks,1,for quick washes,2 for lights.Personally i do see a difference in the clothes-they feel softer too.
Did switch to Asda's own brand liqui capsules-to save a bit of money,but ended up throwing them away-they did'nt dissolve properly+left blue goop on the clothes.
Also did'nt like the powder as it constantly blocked up the drawer opening.x.