Your algae problem is likely tied to your high nitrates. 40ppm is pretty high. Doing more frequent water changes will be a big help.
But, to add to what others have said, you really need to get those
Goldfish into a bigger tank as soon as you can. Are these fancy
Goldfish, or comets? For six fancy
Goldfish something like a 75g would be good; comets would need something much bigger. I wouldn't add the
Goldfish to the 29g as this will overstock that tank. Also, mollies especially are known to pick at the slime coating on
Goldfish so they're not really compatible anyway.