Your fish will be ok. I had a 120 then 240 l aquarium from the age of 16 to 37 although not goldfish but tropical.
I recommend you to put some plants inside the tank even if it is only 2-3.
LIving I assume?
The gravel filtration system is ok for small tank. However, you will need :
1/ To leave the water for 2 weeks before putting a goldfish, it needs to be clean. Else you will have an accumulation of a dangerous chemical (nitrate first then the dreaded nitrite) in the water coming from the degradation of the excretions of your fish (poo in english ?) :celebration:
yummmm amonia! :lick: Can I temper the water with minor water chages like Vomtetia stated?
2/ This system is using the gravel as a filtration mass. Consequently, you will have, if not enough plants, an accumulation of dirt inside the sand. It can look nasty, although not too dangerous for the fish, on the window of your tank.
3/ Try to move to a larger tank of at least 60-100 l and put more fishes, smaller than goldfish, I mean tropical fresh water fishes. Aquarium is a fantastic hobby, not too costly apart from the initial investment. You can even generate revenue through reproduction. I made some good cash when I reproduced ramirezei
Crappie minnows for fishing bait :thumbs up:

Good to hear from you; gas is $3.20/gal now here.
Yup, UGF are excellent, and for the bioload you have in your tank, it's all you will ever need. Be careful though... It starts as a goldfish bowl, and the next thing you know, you're at the local pet shop picking out $100+ reef fish for your new 300 gallon tank.
Add gas expense and their $125. At least Frank Drebin doesn't know where I live!
... and if upgrading to a huge tank (i.e. more than you can easily lift), think very carefully about where you want to put it because they're a serious pain in the bum to move!
Heh, we have an oak entertainment center that we've had for 17 years. It will stay with the house, or be destroyed for firewood. Ain't no way we're moving that again! :rofl: