I have two dwarf hamsters in separate cages, and one has normal dry poop while the other's poop is wet ?

but the wet poo has form, it's not like diarrhea. In the petshop, the hammies only ate pellets. And at home i gradually introduced a mixed seed,nut, and all that other stuff(a hamster food bag with variety is what i mean) diet. They both had a little squishy poop, but then the other one's poo hardened , but my other hammy still has squishy poo. He's healthy and he has had squishy poo since i bought him, like two months ago, but he is active and fine all the time. What should i do to prevent the squishy poo, any food that i can give him because it's nasty if i hold him and he poops squishy poo on me.