Re:Worried new mama

Dear Laurie:

Thanks for the update! It’s great to hear that your new seahorses have perked up again and regained their appetites. I think you’re back on track again, so stick with the smaller frozen Mysis and maintain the increase surface agitation and extra aeration.

Okay, that makes perfect sense now — if your salinity is 31 ppt, that would correspond to a specific gravity of 1.023, which is just fine. You do have a trace amount of ammonia right now but that should disappear over the next few days as your biofilter adjust to the heavier bioload in the aquarium.

Your nitrates are a little on the high side, of course, but it sounds like you’re already taking steps to bring them down. For a seahorse tank, we liked the nitrates to remain below 20 at all times, and ideally below 10 ppm, if possible. Adding the special filter media to your Freedom Filter in order to help reduce the nitrates was good thinking.

Don’t hesitate to leave the airstone in your aquarium to facilitate the surface agitation and oxygenation, Laurie. An airstone cannot cause an ammonia spike, although sometimes it may appear that way. What sometimes happens is that in an aquarium with low O2 and high CO2 levels, the pH is naturally somewhat depressed. When you subsequently increase the dissolved oxygen levels and drive out more of the CO2, the pH will be elevated back into the normal range again. It is actually the shift in pH that can cause a transitory ammonia spike under certain circumstances.

This downward pH shift that occurs in an aquarium with low O2/high CO2 can actually help protect fish from harmful ammonia levels simply due to the fact that ammonia is less toxic at low pH and becomes much more toxic at higher pH. This is because ammonia exists in water in an equilibrium between two different forms — a nontoxic ionized form usually referred to as ammonium (NH4+) and an un-ionized form (NH3), which is highly toxic. Ammonium (NH4+) is completely harmless to fishes since the ionized ammonia molecule cannot cross the cell membrane and enter their cells. Note that only difference between harmless NH4+ and deadly NH3 is the addition of a hydrogen ion (H+), which converts toxic ammonia to nontoxic ammonium. At low pH, the extra hydrogen ions (H+) of acidic water are readily available to attach to the ammonia molecule, converting most of the ammonia to ammonium: NH3 + H+ —> NH4+. But at high pH, under alkaline conditions, exactly the opposite occurs. At high pH, the abundance of hydroxide ions (OH-) in alkaline water strips the extra hydrogen ion (H+) away from ammonium, rapidly converting most of it to deadly ammonia: OH- + NH4+ —> NH3 + H20. In other words, the higher (more alkaline) the pH, the more ammonia is present in the dangerous un-ionized form (NH3), which easily crosses cell membranes and enters the body.

So if an airstone races the dissolved oxygen levels and drives out more carbon dioxide from the aquarium water, this will tend to raise the pH, and a significant upward shift in pH can convert harmless ammonium in the tank into dangerous ammonia. But that shouldn’t happen in an established aquarium where the nitrifying bacteria can easily convert all of the ammonia into nitrite and finally nitrate as fast as the ammonia is produced. And if the pH in your aquarium is currently a little above 8, then adding an airstone should not significantly alter the pH, and there should therefore be no increased conversion of ammonium into ammonia. In your case, I would say that it should certainly be safe to leave the airstone in the tank to promote efficient gas exchange at the air/water interface and raise the levels of dissolved oxygen, which is something that your seahorses seem to be responding to very well.

Best of luck with your new arrivals, Laurie!

Happy Trails!
Pete Giwojna