I was not really sure where to post this question but since most of the analytical people seem to be in the environmental field, I was hopping that at least a few of you work in labs that do have a bioassay department.
We use water for this assay obtained from a local lake that has been tested and screened and approved by our state. Each time when the supply is running low, our bioassay scientists have to go out to this lake with a few carboys and collect more water. Before we can use this new stock of water, we have to do some elemental analysis of the water to ensure that there are no metals that are over the maximum limits established by our state. Usually it is not too big or a problem but currently we are having an issue with the latest stock having aluminum content that is much too high. We have tried pulling the sample from several points in the lake as well as shallow points and deep points and the aluminum levels are still too high. I believe that the reason for the spike is related to the massive pollination that is now occurring in our state. However this still does not help us out as there is really nothing we can do about the course of nature. We also do not have a secondary source (lake) approved for use.
So I am trying to find some options for eliminating or greatly reducing the aluminum content within our water while not compromising the nutrient level or adding compounds that could effect the growth and health of the organisms that we are testing (fathead minnows and water fleas). We have tried a carbon filter and it did reduce the aluminum level somewhat, it did not reduce it enough. I am considering using RO filtration but I was not certain if this would also filter out all of the nutrients.
If anyone can just provide me with some suggestions or ideas regarding what we could do to resolve our issue or share your experiences in bioassay which are similar to ours, then that would be greatly appreciated.