My 3 starter danios have suddenly turned shy. They were active for the first 2 weeks but now they’re spending most of the time hiding. Sometimes, they'll re-emerge when the lights are switched off. I don't get it. Water parameters/conditions are at optimal levels, they’re eating and there aren’t any noticeable signs of parasites/disease. Any tips on to solve this situation? Is it simply because they need more company (perhaps 3 more danios)? I plan on getting more...I just don't want to overwhelm the bioload.