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ok so i have 3 RES and every few weeks i see that there shells have algae on them so how can i wash the algae off theirbacks i usually use an old toothbrush with warm runnung water to wash it but not sure if it's right!!(thx)

Welcome. Gently brushing with a soft brush is fine. I've also wiped the shell with a soft cloth to clean the shell.

Is there a lot of algae in the tank?

yes there is alot of algae in the tank too but i have filter already though thx anyways.

Having a filter isn't directly related to having algae (but a filter that's not powerful enough for the tank may contribute to it). If the water is clear but you have some algae on objects (the edge of the basking area, rocks, for example), that's fine. If, however, the algae is out of control, that's another story. I was wondering if the algae was growing everywhere and was taking over the tank.

oh no it only on rocks and stuff thx
but should i brush the shell softly or hard

Gently, not hard and brush in the direction the scutes/plates are growing. They can feel through the shell, especially in the areas in between the scutes (the seam). I have, in the past, used q-tips to clean those areas, especially with smaller turtles.