A few months ago I inherited a beautiful 30 year old cactus. I was given instructions to water it thoroughly once a month which I have been doing. The cactus lives by a large window so gets plenty of natural light. It had a few brown spots on it when I got it but I feel like it is just not looking very happy or healthy. Hoping someone has some advice for me! It also was a bit dusty and I've tried to clean it with a sponge and water but hoping someone maybe has a better cleaning solution for me.