Cynops pyrrogaster strange action

Hello guys.
my Cynops makes a strange action .. and as usual I terribly alarmed.
is located in a land-aquarium of 60 liters without filter.
I change the water every 15-20 days.
* is two days I see him two strange movements.
the Cynops arches his back, Leaning one then its cloaca in contact with the base of the aquarium, then doing two three steps.
after this he turns to the cloaca and strikes a little bite
this occurs for about an hour, however, not below, but in an hour ago this show a bit of times.
then back to his old life
I'll post a photo .. and I hope to do another picture during the performance.
I'm afraid I have some infection!
ps: did the suit twice in 2 weeks, it can serve

Could the newt be scratching its bottom? It would be great if you could post a photo.

I would definitely recommend some changes to the aquarium - plants and some sort of decorations would be good - it just looks incredibly boring for the newt. If there is no lighting then you probably can't have plants but Java fern and Anubias can live with very low light and don't need substrate. You could definitely add some rocks or some driftwood. The decorations will also be good because beneficial tank bacteria can live on the surfaces and help to keep the water quality good.
I'm not sure I understand correctly but if you change all water every couple of weeks, then you are always resetting the cycling process. A partial water change (25%) every week would be better. Have a look at articles about housing and water quality here.

I wonder if he is shedding, mine sometimes do a similar move to try and dislodge the skin. I agree with Eva that the tank could do with plants etc.

thank you for your answers
I now buy a anubias and try to put the stones.
sure is difficult for me to accept that the itching of Cynops, is due to the lack of equipment in the aquarium, it seems strange that the animals are so simple even so capricious.
I put pictures of the cloaca hope are clear

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[IMG=http://img26.**************/img26/5907/dscn0209d.jpg][/IMG]

How often he behaves like this?

He may be shedding his skin. Watch him closely when this behavior happens. If he is shedding his skin you will be able to see the skin when the newt pulls it off himself. Our newts eat the skin right after they shed it and the swallowing always takes a while.

I hope there is a harmless explanation and your pet is not sick.

I put in a plant and rocks ... the Cynops has never done this unusual move.
Now the water is clear and she is more quiet