HelpfulGardener.com

Hi there. First post on the forum! I've had this cactus for about 10 years,it started life about 3cm tall. I report it gradually as it outgrows its pot,water it once a week in the summer on the window sill,and in winter I take it out direct sunlight and only water it once a month or so. I've noticed that in the last month or so it's started to go yellow as the base. Any suggestions? Shall I re pot and give it dry soil incase I've overwatered it by accident?

I have just removed the cactus from the pot to see if the soil was wet/sodden. It was barely damp to the touch. so a tad confused as I thought it may be rot