Goldfish will eat any fish they can catch which is small nough to fit inside of their mouths. Your tank is overstocked though for a goldfish tank, with algae its best to find the source of the problem and deal with it there- the most commonly sold types of "algae eater fish" or "sucker fish" are sailfin and common plecos, chinese algae eaters and hillstream loaches, all of which grow massive, or very agressive or need very specialised and expensive tank set ups.
Always thoroughly research your fish before you buy it, otherwise you could end up with a monster or very costly fish on your hands.
i didn't think it would fit inside their mouth though
the goldfish have grown quite a bit.. i may need to buy a bigger tank yeah? algae is not an issue here.. i just thought it would be nice to have an algae eater fish... i did ask the store pple if it's okay to put it in a goldfish tank.. maybe it jumped out of the tank?
Asking people at the store doesn't really count as research- they are there to sell fish and stuff to you, its no wonder they sold you an unsuitable fish (regardless of what the fish was, there are no coldwater algae eaters suitable for a 5gal suitable to live with goldfish), afterall they are just there to make a sale. Most fish store staff know next to nothing about fishkeeping since there training will not really cover it (they get paid so little, the job doesn't justify it)- a car salesman will not tell you how to be a good driver just as much as petshop staff are no more obliged to tell you how to be a successful fishkeeper.
So you really need to do your own research, and thoroughly at that- there's so many ways you can go wrong in fishkeeping and end up causing your fish unesarsary suffering or stress or even deaths.
Well my goldfish are doing gr8 with other fish. They are all happy and healthy.
Your tank is just under 6gals (5.81 US gals), but its probable volume is 5gallons. This is too small for any goldfish, fancy breed or not- all fancy breeds of goldfish (such as yours) can grow to 6-8inches long, while non-fancy breeds can easily grow to 10-12inches or more. So a 5gal tank is no place for such large growing and high waste producing fish and to be honest is very overstocked.
Overstocking a tank will result in stressed fish, greatly increased chances of poor water quality/water quality issues and greatly iincreased chances of desease and parasite outbreaks, which will also be more difficult to treat.
Goldfish kept in such a small tank will result in stunted growth and a greatly reduced life expectancy, poorer health and quality of life.
It is difficult to judge "happyness" in fish since they do not exhibit a great variety of emotions in comparison to a lot of other animals, they may be friendly and tame towards you but they will certainly not be very healthy in a tank that small and if they have been in there a long time, will probably also have retarded growth/development to a certain extent as well which will have a negative impact on their health and quality of life.
So basically you really need to upgrade their tank or rehome them to someone who is more capable of looking after them properly if you cannot give them a larger tank with improved filtration- it is your duty to as a responsable fishkeeper. If you are mixing tropical fish with your goldfish (which are sub-tropical going on coldwater) then that is also a problem. In reality, it is very easy to overstock a tank of 5gallons if you do not research your fish properly or go along poor petshop advice.
For fancy goldfish stocking, you should have 20gallons for the first fancy goldfish and 10 for every one after that. In a very large tank (say 75gallons or more), the "rules" can be bent a little if the tank is very long and there is very powerful filtration in the tank.
Goldfish grow big and produce a lot of waste- they are no less important than any other type of fish or animal, and so should be treated with care and respect. Too many people buy goldfish and stick them in tanks far too small only to find they die within days/weeks/months/couple of years, which is bad when you consider that they can easily live to over 30years old given the right sort of care and environment. I appologise if this sounds like a bit of a rant, but you need to know the facts- trust me, a fish which can potentially grow to 8inches long kept with 4 others of its kind and an assortment of other fish kept in a tank barely over two bucketfuls of water/20litres is not going to be happy even if it loves you.
So my main advice to you right now is to upgrade their tank to at least a 40gal long tank for the goldfish, ID the rest of your fish and give them a suitably sized tank (since there is not a very wide range of coldwater fish, it is likely your other fish are tropical) and do lot of research on general on keeping them and the tank healthy and properly cared for/kept in general
. I am sure you will make a good responsable fishkeeper if you are willing to make the important changes to your current tank set up for the better- it will be in the best interests for the health and quality of life of your fish
.
(The algae eater could have died of anything considering the tank is overstocked (which could have created the environment for a lot of things which led to the new fishes downfall), it was never going to adjust/acclimatise well to your tank as it currently stands and would probably have not lived very long either way unfortunately.).
