Foam can and will develop in perfectly balanced hot tubs. If it has been more than three months since you have drained your tub, you may consider draining and rebalancing at this time. Another alternative, is to purchase hot tub defoamer. It works instantly!
Sources of white foaming may include (but are not limited to) a build up soap film, detergents, cosmetics, deodorants, etc. Brown or tan foaming needs to be removed as its organic contaminants build up and can cause issues.
Sometimes water chemistry in a hot tub, such as high pH and/or low Total Hardness, can cause foaming. Test strips or a water analysis from your local pool store can help determine if one of these are the cause of the issue.