Cyanotoxins, could it effect my animals? How risky is over dechlorinating water?

[Hypnofrog]

For the next week or so my water will be contaminated with low levels of cyanotoxins, not enough to harm a healthy adult but babies and the sick could be effected, also pets. I don't know if this could have an effect on my stressed juvenile frog or my leopard gecko, or even my dubia roaches, all of who already received contaminated water thanks to my helpful city not mentioning it for a week, albeit toxins were at very low levels at the time.
My only other water option is a Brita or something similar, a carbon filter that's effective against cyano/toxins/bacteria/things, but home filters are also supposed to have a negative effect on amphibians over time and since I don't know if the water here contains chloramines I'd need to treat it and I don't want to over treat it since the filter also filters out chlorine..

So basically I don't know which water source to go with, I'm leaning towards using the carbon filter since it's most likely only a few days until the water is back to normal, unless over treating water with dechlorinator could be dangerous. And how much would I want to use on maybe a gallon of filtered water if using tetrafauna dechlorinator for amphibians and reptiles?

I also have a little water left from when the cyanotoxins were very low, but it's been sitting around so maybe they grew?


Bottled water is no longer available anywhere.