Will Extra Filtration Compensate for an Overstocked Tank?

[OrionGirl]

I don't think it's a great plan to just 'watch for the fish to be stressed.' By the time stress is causing visible symptoms, it's already negatively impacted the fish, from which the fish may never recover. For example, one side effect of stunting is that the organs continue growing inside the fish, eventually compressing each other. At some point, this is fatal, even moving the fish to a larger environment is a case of too little, too late.

Some light reading:
http://www.seriouslyfish.com/stunted-growth-means-stunted-lives/

 

[tanker]

Are you over stocked=No. IMO, a 75 can hold up to 9+ "Fancy" Goldfishes, but you will need keep up with the large WC. I think, so far, you are doing fine, but like Bishop said "remove the Comet".
Filters convert the Ammonia to Nitrites and then to Nitrates. There are many ways to remove the Nitrates, but the best is with the large WC that you are doing.

PS--Thank OrionGirl--very helpful knowledge.

 

[SantaMonica]

Yes, stocking stress is very important. But of there is an ammonia spike because of a large feeding (common when many new fish are introduced), and the filtration is not sufficent, many fish will die in a few hours.