pull them outside of the water, spray on them diluted dish soap with a fine drops sprayer. wipe gently with a cloth. dilluted dish soap will attack the waxy epicuticle of the aphids. \it is not dangerous for the fishes if it is very diluted. At the contrary - it is rich of phosphate qhich can be good for the plants
Thanks for you answer Susanne, but aphids are damaging plans, they wit them. Althought I did not know that they could control other pets, which ones you mean?
Thanks also for Javaid, I will try with soap, water pressure did not work, I tried that many times and aphids remain.