Hi.
Feeding in the dark will make a big difference, as these catfish are nocturnal. They will eventually come out in the day, but it takes while.
Try feeding an hour or so after you turn the lights out.
Cucumber is not great food for
, as they are generally meat eaters. They prefer things like bloodworm, cockle and shrimp. A really good food to try is Hikari algae wafers, which despite the name are mostly made of fishmeal, which the L260 love. These algae wafers are also big enough not to be eaten by the danios.
The L104 is
, and in the wild eats wood. You should provide soft bogwood for him to munch on. He will also eat veg like courgette, broad beans and sweet potato. The L260 will also eat a bit of veg too, sometimes.
Bear in mind that both these plecs need pretty warm water to thrive (above 27C). Below this temp their metabolisms don't seem to kick in, and they often don't live very long.
Another point to mention is that you are at a very delicate stage, as you are still cycling your tank?
It is very common for people to set up a tank, buy a fancy plec before the tank has settled down, not have the water warm enough, wonder why the plec is hiding and never eating, add loads of different foods they read about on the web, and hey presto one dead plec from ammonia/nitrite poisoning.
Be really careful with the amount of food you add, as rotting food will kill these sensitive fish quicker than you realise. Add no more than about a quarter of an algae wafer and always search the tank for uneaten food the next day. Test the water too....
Let us know how it goes.
Will feeding the Plecos in complete darkness make a difference ? I always put cucumber in after lights out with most success, but then even with lights on the Danios arent interested in the cucumber. I have some sinking pellets that are too big for both Danio and Tetra yet they still get nabbed !
By co-incidence ive just put some broad beans in the tank. Any veg i put in is being removed the next morning. 
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