Toilet cleaning- with septic tank

[Methenyouplus4]

We can't put bleach/anything harsh down the toilet as we have a septic tank. I've just been using a bit of Ecover washing up liquid and toilet brush which is fine on downstairs toilet (really old ceramic toilet) but the modern upstairs one we had fitted about a year ago has horrible yellow/brown stains on it.

Any ideas?

You can buy toilet bombs, they dissolve limescale which is what the stains are sticking too. I have no idea who they are made by but you can buy them at all supermarkets X