Turtles

I have two yellow belly sliders, ‘the boys’.
They were brought in from the garden pond 6 weeks ago and I am happy with their set up, docking platform and lights all in place.

The shells of the two are markedly different, the one is very healthy, this would appear to be the dominant one of the pair, usually at the food first.

The other has shell with an appearance much less healthy, some sort of algae or slime covering, and there have been shell pieces which have fallen off, but I have dismissed as something which should probably be expected.

I have wondered whether there might be something missing, or whether there is something I should be doing? Light scrubbing with a clean toothbrush? No doubt this would cause some stress.

Only the dominant one positions himself on the dock from time to time for a dry out and sunbathe under the heat lamp. I have picked up and placed the sub turtle but he scrambles for the water every time. So he has not had a thorough drying out for goodness knows how long. I wondered whether I should take him out of the tank for an hour or so inorder to facilitate this?

The strip lamp for UVB is the same one I used during the winter of last year, I suppose these might only have a finite life ability to emit a light effective for them. I have it positioned above the tank and parallel with the rear side of the tank, so perhaps some rays are not efficiently directed?

From time to time in the past I used to coat some food in a calcium powder, which was given to me by their previous owner. I have not done that this season.

Food is regular turtle pellets, sometimes only every other day, fresh veg clippings like carrot and brocolli, potato, cucumber occasional fish and odd treats from our dinner table leftovers. I had read somewhere that they are partial to tinned dog food.

I have some dried mealworms but the tub is two years old. They are no sharing accommodation with a guppie but they show demonstrate no appetite for it. I wonder whether some other live foods might be helpful?

I've recently bought 3 unwanted Sliders. When I first got them their shells looked like they were almost flaking in some areas, which I've now learnt is normal, like a nail growing, its just making new layers which is good especially if the one with the slimy shell is doing this.

I've heard that brushing the shells lightly to clean them can help and rubbing olive oil into the shell after is meant to protect it. You might want to check that though because Im not sure if thats just for Tortoises or if you can do it with turtles too.
They may need a good clean from being outside in the pond.

How big is the basking area for them? I've got 2 boys and 1 girls and they all have a dinner plate sized rock out of the water with a uv basking light on a few hours of the day. They absolutely love this and will climb on top of each other to try and get as close to it as possible! It's mainly on in the evening because I don't like to leave it on unsupervised just because of how hot it can get and being so close to a wooden lid. You can get these in the reptile sections in pet shops.

It may also have a slimy shell due to the filter not being strong enough for the amount of water the tank has.
I find that taking the filter out every week and taking it apart to clean throughly makes a big difference to the cleanliness of the water.
Also every week I will take out 2 buckets worth of water and replace with 2 fresh buckets of water. This helps to keep with water clean with out disturbing the set up and also the tank and rocks are really heavy to move around.
Maybe trying some of these may help your lil fella