starter growing red mould

With help from the bakers here I started a sourdough starter about 3 years ago and it's still going strong, stronger in fact than before, it raises bread nearly as fast as dried yeast. 

There have been times I've had to leave the starter for a few weeks and it's developed pink patches of what looks like me to be some kind of mould. I've never worried about it, fed and used the starter. In the last month even though I'm using the starter every week it's developing patches of this pink mould most weeks and I'm at a loss to stop it happening. My technique is to take all the starter, double it, double it again and then take 125g of that rich bubbling starter, feed it, let it sit for an hour and then fridge it. I've found that gives me a really strong culture. I've carefully ensured I have a fresh clean container each week but still I'm getting a sheen of pink mould after just a week in the fridge now. I feel the starter has moved out of balance between yeast and acid and I need to do something different to keep it in balance. 

Are there any suggestions about what to do to get my starter into balance before fridging it? Am I by taking really active starter to put away not letting it develop the acids it needs?