I do not think it has much of an affect at all. It is a very low ph, maybe even check it if you have the means. Soak some peat in water for a week or more, then test the ph. I believe it doesn't get below like 6, that might even be to large of error on my side. Some tadpoles, like those of some mantella's, like the water to be slightly acidic. So, unless it is a really low ph, I do not believe it to be harmful. I am no pro though, I am sure someone who really knows for sure will chime in.