It is, but how are we supposed to help you if you won't listen?
They will never outgrow the tank because they will be stunted. Only two fish can live safely in that tank, that's what we've been trying to tell you all along and you yap on about crystal clear water and ornaments

Mohannad, I appreciate you love your goldfish, but you have to realise that a 100 litre tank is not a permanent home for them. They will become stunted and could have health issues because of the over crowding in the tank.

So once you take the 4 sharks back to the pet store, you will have the goldfish to deal with.

Firstly you have mixed single tailed goldfish (the comets) with fancy goldfish (the moors and fantails), generally this isn't the recommended because as you can see, comets are more stream lined and faster moving than the moors/fantails. This can result in them out competing the fancy fish for food and may also cause stress by their quick darting movements, compared to the moors/fantails slower 'waddle' type swim.

Single tailed goldfish do much better in ponds, or very large aquaria, I imagine you have juveniles right now, but they can and will grow to 1 foot in length. Unless you can provide a pond or aquaria of at least 6ft x 3ft, I would suggest you look into re-homing both the comets. Perhaps someone near you has a pond? Or a local park or botanical garden has a pond that accepts goldfish? Just a quick note though; Do not release the goldfish into the wild, it's illegal to release fish were they aren't native, so don't go releasing them into any streams or rivers.

Myself, I currently have a single tailed goldfish and I'm in the process of organising a pond or another home for her. She is a juvenile, barely 3 1/2 inches and currently has a 90 litre/3 foot tank to herself! This isn't big enough for her as she will out grow it and I cannot add another fish, because it would over stock the tank. It demonstrates how much space these fish really need. It's hard to believe looking at her when she's so small, but remember fish do grow  

Now this will leave you with the 6 fancy goldfish.
The general minimum rule for stocking fancy goldfish, is 20 gallons/80 litres for the first fish and 10 gallons/40 litres for each additional fish. This is the basic minimum requirement and will ensure the fish have plenty of space to grow and have room for exercise.
So for your 6 fish you would need a minimum tank size of 70 gallons which is roughly around 310 litres. Preferably one that is 3 or 4 foot in length, so they have lots of swimming room  

The 100 litre tank will make do as a temporary home, if you were to organise the larger tank for them

If that's not possible, then again, I'm afraid you would have to re-home them or take them back to the store. You could then always set up your 100 litre tank as a tropical set-up, there are lots of fish that could live happily in your tank permanently, it's just that sharks or goldfish aren't one of those.

Let us know how you get on and if you have any further questions. Best of luck!

I kept fish on and off from the age of six and same as you didn't know this info. Keeping fish is hard work and relatively expensive to begin with. You obviously love the fish which is why you wanted to keep them. I'm sorry if some of us were harsh but sometimes you have to be hard to get people to here what they need to. I think in the end you will make a great fish keeper.

Or in this case, which is more likely: They won't manage to grow properly in such a crowded and small tank, meaning they'll stay there until they die. I really don't like the idea of giving them away when they grow. What's the point in keeping them in the first place then? Why not just buy a bigger tank and sell the current one to fund a new setup and keep the fish healthy and happy?