Fish all grouped together at corner of tank

[Philomena]

My fish are all grouped together in a corner on one side of the tank. They are coldwater fish. It's a 120L fish tank. Its a mixture of fancy goldfish abd common goldfish. Could anyone give me advise on why they are doing this ?
I have attached pictures.

[axolotlgirl]

Did you just get them? How long have they been doing this? Do they react to food?

[Philomena]

They been doing it all day yesterday. 5 of them are new. And the rest are 6-8 months old. They react to food and come out for it.

[coralbandit]

Adding 5 goldfish at once may cause a 'spike' in your biological filter causing ammonia or nitrite to remain in water column ?
Can you test for ammonia or nitrite ?
How often do you change water and how much do you remove ?
I might be inclined to do a water change just for safety after adding fish every couple days for week or so...

[Philomena]

I do a half clean out ever 2 weeks and a full clean out ever month. Is that too much ?
I did a half clean out on Monday but had to do a full clean out last night cause the tank looked dirty. Maybe that was from adding to many fish at once in during the weekend ?.

After the full clean out last night l noticed, this even they are starting to move around more and more lively. I also added in an extra plant that is helping also.

Thanks everyone so far who has replied. Really helpful. I'm new to keeping fish tanks. So all the help is great.

[54seaweed]

gold fish are ammonia factory's you need to check your ammonia and change out water as needed.
120 L = 30 gal 5 new gold fish on top of what you had is quite crowded
I suggest bigger tank , or pond or bring them back , with that many gold fish you will be doing daily water changes for sure .
large amounts of ammonia will deplete the oxygen level in the tank , the fish will start to die off .
this is a very good article that you should read it may help you better understand the problem.
ammonia-poisoning-1378479

the dangers of over crowding this may help better understand
dangers-of-overcrowding/

[Toad]

I'd return the fish you bought and then figure out how to deal with the fish you already had, goldfish get very big as it is and the tank is too small to really do goldfish in :/