Hello everyone. This is my sand bed. 6 month old tank. Looks like diatoms on top (which is new) but under the sandbed is tons of green algae and those weird lines. I added a diamond goby and noticed my nitrate spike up to 70 so I blamed him for that. Now I believe he died because he is now where to be found and my nitrate is testing 75+ because the Hanna checker only goes up to 75. I have to lower nitrates and I believe I need to clean the sand and then do a large water change. Could anyone steer me in the right direction so I don’t make a catastrophic mistake??