Posted: Thu Apr 21, 2016 1:06 pm Re: Hard White Substance
It is a egg, unfortunately some will drop eggs in the water unfertilized as mentioned and she may be going to drop more. Even when a nesting area is provided, sometimes they will still let them go into the water and others will use the nesting area. I would double check the sexes but yes females can do that without a male present.
Confirmed Sexed Pair of Albino Red Ear Sliders, Baby Albino and Hybino Red Ear Slider and Adult Normal Male Red Ear Slider