Your frogs don't actually need lighting for health reasons as much as having a day night schedule and heat if needed. If your room provides enough light to indicate to the frogs when is daytime and when its night, then your all set as long as you meet the temperature needs of the frogs.

As for the cleaning, it is the water sharing, and the where I sat/walked you sat/walked soon after issue. Poisoning doesn't happen all at once but over time as each absorbs minute amounts of trace left behind by the tank mate.
Its the difference of between having a frog live 2 to 4 years instead of the 10 to 20 he should.