I expect you won't like what I'm going to write here, but I love goldies and always hate to see anyone else who also does, watch their beloved pets die, because given proper care, any goldie will live for many years.

14 gal. is barely enough for one, let alone five goldies. Also, in what configuration? If the tank is taller than wide, then it's wrong for most any fish, particularly fat goldies. The old so-called "standard" of a gal. of water per inch of fish is just so much hooey. The real criteria is body mass and even a baby, 2" moor will bulk out to the equvilant of several dozen guppys.

Meanwhile, as long as the filter isn't causing them to struggle against the current, the heavier the filtration the better and while with strong filtration, airstones are usually unnecessary, for goldies, any means of providing more oxygen helps.

But in any case, 5 goldies need far more than 14 gal, so for the present, until you can get them into a far larger tank; light on the feed and a min. of a 50% water change at least 2x weekly is your best defense against dead fish.

The problem with goldies in pet stores is that they seem to be doing fine crowded into smaller tanks, but in large commercial set-ups, the tanks are being filtered with a flow-through system large enough to run a 10,000 gal. pond and continually fed with fresh water. The closed system of a single tank is another matter altogether.

So enjoy your moors and as they grow, plan on setting up at min. a 55 gal tank for them and unless you want to do a 10% water change daily, with a filter rated for at least a 125, or more.