One of my fish is stressed and the other is constantly following it?!

[wj2]

Weird behavior coming from my two Comet goldfish.
Just for reference: I am positive that they are male and female as I have had them for 3 years and Snapper, who i suspect as the male, is much bigger than Moki, the female.

Today I came into my room to find Snapper following Moki around the tank (which is 40 litres by the way) unusually as well, Snapper was like sticking to her side, and some of Moki's scales had been scraped as a result of previous chasing and part of her tail bloodshot.
Moki is clearly distressed.
I just fed them incase they were hungry, and Snapper stopped chasing Moki for a bit.
Now Moki is swimming away from Snapper very fast and hiding from him, and Snapper is acting slightly aggressive. I have heard about males chasing females around tanks, but not to such an aggressive extent..

Any help immediately would be fantastic! I really would like to know what is going on as I am deeply confused and concerned.

 

[Sharpchick]

First of all, a 40 liter tank (10 and a half US gallons) is not nearly large enough for two 3 year old comets. The aggression you see is probably related to water quality and size of the tank.

Comets are pond fish. For indoor aquaria they need a much larger tank to be healthy and happy.

 

[SKB]

I agree with Sharpchick, any type of goldfish aren't known to be aggressive but since they are in such a small tank, this might be a result. Comet goldfish should be in ponds and usually grow to the size to be in one. I know you don't want to hear it, but its a good excuse to upgrade fish tanks!

Either way, if you can find someone with a pond, that would be ideal.

 

[Fresh N Salt guy]

They are very large fish for that tank. I'm not sure of the size of your fis but a larger tank is definetly necessary in the near future. You may buy a little time if a new tank isn't in your budget by adding large plants to the middle of the tank and a rock or two that the smaller fish can fit in but not the large one. Use the plants to break line of sight from each side of the tank so the larger fish can set its territory on one side leaving an open side for the smaller to inhabit. This may buy you a few months since it seems to be a new issue in the tank. One cheaper option is to set up a large Rubbermaid bin up as a makeshift pond indoors. A simple 100 gallon rebbermaid bin, about $25-$30 can easily be converted into an indoor pond running filters, heaters, and aerators just like an aquarium. You'll lose your side view of the aquarium but a cheap alternative to losing your fish. I did this with two large florida softshell turtles which I keep pretty large coi with them as well. Either way, money will have to be invested to keep these fish healthy and alive