Well,

The fluorine in alkali soils and water containing large amounts of organic compounds has a greenish yellow color that is more stable in the little concentration and to dissolve the dye, the soda and the ammonia are added in a small quantity. A limited amount of fluorine is used for each type of soil or rock.

Regards

Clay minerals have permanent negative charge. Thus you do not need to worry about adsorption of bromide; rather, there could be anion exclusion. Nevertheless salt tracers (NaCl, KBr) are widely used in this kind of appication. You may trace them either with ion selective electrodes or using a conductivity probe. Maybe the attached paper is useful to you

it's good

I agree and recommended answer by Harald Weigand .

I agree with Harald.