Weekly waterchanges in an adequately sized tank might be enough but in a 1 gallon... it's not. Are you able to upgrade the tank to a much larger one to house these 2 goldies? If you are not able to... you may be best to rehome them (or return them to the store if that's not possible). They will not do very well in a 1 gallon... who will literally bust out of that before too long. I'm sorry to say that the minimum tank size you need for the 2 goldies is 20 gallons (to handle their size and waste they expel)... and even that will likely be too small as they get even bigger. If they're comets... they can easily grow to 12"+. It's a myth that they will only grow according to the tank size they are in. They can become stunted, however, from the lack of space and poor water quality... which is a miserable life for them either way if kept in small confines.

I'm sorry they won't do well unless the their environment is changed.

Michele