bubbly slim on top of water

Question
There is a bubbly slim floating on the water. I have 135 reef tank. I have tested the water. It is all good, also temp is at 78. Noticed it a day after water change. Also protein skimmer seems to be working harder. Please help. Thank you for your time.

Answer
Hey Louie,
It could be a couple of things. 1, it could be protein, and will start to show in water tests in another day, or 2, and more likely, it could be your water conditioner. I assume you use a water conditioner with RO/DI water and your sea salt mix? Most of the conditioners on the market(especially those with bacterial content)contain additives that are lighter in density than water that will float and become a bit bubbly or foamy(especially if we add a bit too much). Even if the concentrated conditioner sinks when added, after mixing it separates in the system(this is what its supposed to do). It can also make the protein skimmer work a bit harder as it gets treated by the skimmer as protein. It usually subsides in 3 or 4 days depending on water flow and filtration in your system. If ammonia, nitrite, and nitrate are all 0, that would be my best guess without seeing it. If you have even the smallest amount of ammonia, nitrite or nitrate they can also appear in this manner. When we do water changes in our systems we disturb the biological filter. It's unavoidable. It then takes a few days for the biological filter to get back up to speed, especially so in systems larger than 100 gallons. I see it quite frequently in my larger systems. It's generally nothing to worry about. Just test your water again in another day to make sure, but it should start to disappear by then. Let me know how it goes.