Redish Brown Water

I have a pond that has goldfish,snails and tadpoles in it, and several
waterlilies. The water started turning a redish brown color. I checked
the ph and its just a little low. Has anyone ever had this happen or
can tell me what to do to get rid of it. I dead headed all the flowers
that bloomed and had taken all the yellow leaves off . I am stumped
about this. My husband says to bring up the ph and it should be ok.
Please let me know! Paulette