hi lads i have question about a air powered protein skimmer
they are good for a 200l tank?

when i was first setting up my tank and was trying not to spend money i was recommended to get a berlin skimmer (think that was the name). anyway it ran on an airstone (wooden airstone) and could be hidden in a juwel filter box. never bothered so i cant say if they are good or not. i think platy252 has a reef tank without any skimmer so you might get away without one.

i buy a red sea external skimmer in usa for 30$ - what do you think about prizm?

I would keep the $30 in your pocket and leave the prizm in the states.
If you feel you need or want one i would go for a Deltec. They get good reviews.

and they are very expensive also, i have air pump powered skimmer as a backup,
prizm cost here 200 e, then if they are no good why they are so expensive ?

I don't know why they are so expensive but i do know of 2 people that bought one and ended up replacing them within six months.
Why not use the air driven uplift skimmer you have? Run it for a month and see how much it is removing at the end of the month. If it is pulling very little from the water i would do without a skimmer. If it is pulling plenty from the water then i would invest in a decent skimmer.
I am running a tank with no skimmer for a past 3 years with no problem. I only use a surface skimmer to remove water from the surface to the filter.

this skimmer give me a half cuf of yellow fluid in 3 days of run, but i cant drill the tank and i temporary cant make a sump, this skimmer dont look nice in a tank,
i just want keep 2 more fish in (now i have one blenny and six line wrase)
and just soft corals and small crabs and ad 5kg live rock more.
i know from the other sources if the prizm deluxe is too week for a 400l tank.
mayby for juvel 180 will be ok, the skimmer with shipment will cost me 25 e if will be no good i sell it away or excange a pump.
how big fish tank do they had?

I don't think it was the size of the tank that was the problem. They just didn't think it was worth buying as it didn't do a good job skimming.
When a tank is first set up with new live rock you can still get a little die off. The skimmer will help remove some of this. In a couple of weeks you may find there is less in the collection cup.
If it is only €25 it is worth trying. Although if they sell for €200 why is it only €25 second hand?

my girl friend sister is in usa now, brand new cost 76$ only, and 140$ for a big one for 1200l tank, then 30$ is a half price of the new one,
you can find loads of cheap skimmers their,
i use to design equpiment like that durning my study, if prizm will be crab i will buy a materials and i make my own skimmer

Sounds cheap enough. Go for it.