Hiya and welcome to the forum,
Firstly, yes a bigger tank would be great, 3 gallons is far too small for anything. I can appreciate your on a budget, but have you considered looking for second hand tanks? Sometimes they can be extremely cheap or even free!
Please try and look for one, the reason for larger tanks, is because when kept in a smaller tank a goldfish will become stunted and potentially have a shorter life span.
I can understand your situation, I've been there, I had a goldfish on her own in a 5 gallon tank, but I was lucky to find a 29 gallon tank, which believe me she is so much better off in as she has much more space to swim now. But as a result of being kept in the 5 gallon for a short period, her growth has slowed considerably, I believe she must be around a year or a little older and she is barely over 3 inches!
But she is doing much better in the bigger tank and believe me, it is so nice to be able to watch them swim and spread their fins out without bumping into the side of a tank that's too small.
As my goldfish is a common, she has the potential to grow to 10 or maybe even 12 inches!
Even the fancy varieties of goldfish can grow up to 8 - 10 inches! So these fish need a lot of room
May I ask what type your goldfish is?
Now sorry, I deviated from your question, I am not sure on the Crystal Clear product you mention, but in my opinion a water change will be much better than adding chemicals into the water.
As goldfish are extremely messy then a decent clean of the gravel and a water change of 50% per week is the recommended on here. When I had Lucky in her 5 gallon tank I think I must have ended up doing more 80% each week, just to be sure I'd cleaned the gravel properly.
I'm afraid as a fish keeper, weekly maintenance is just something that has to be done