How many goldfish can i keep in my 30g?

Question:

I'm also planning on replacing my Penguin 150 with a marineland HOT Magnum filter.

Answers:

Goldfish are playful fish each with their own very unique personalities. That's why they should be kept in pairs as they don't do well on their own. However, your 30g tank is only big enough for one fancy goldfish, I would recommend returning one to the pet store. Don't even think about adding a third.

Though I bet many people will soon follow protesting no, I say you can, it's possible especially since they don't grow as rapid as feeders.

2 is good, but you may be able to fit one more.

40% water change every week. I have a python hose hooked up to my R.O water system and I slowly change the water as not to stressed out the fish. I also add microbe lift with every water change and maintain the correct salinity at all times for freshwater fish using aquarium salt.