Are low oxygen levels killing your fish?
Low oxygen levels in saltwater aquariums are a common reason why fish die. It can easily be overlooked but it is one of the more important factors when establishing a healthy environment for a saltwater aquarium.
What are the symptoms of low oxygen levels?
Oxygen deprivation can be identified by the following indicators:
1. Fish with open mouths
As your fish struggle to obtain the dissolved oxygen in the water they require through their gills, they will begin swimming with their mouths open, or open and closing them. This would be particularly evident in larger fish such as tangs.
2. Gills moving rapidly
The purpose of gills is to draw in water and use the dissolved oxygen available. If the water is lacking in oxygen their gills will move much faster as they try to move as much water through their gills as possible with the purpose of extracting whatever oxygen they can from the water column.
3. Staying near the surface of the water
If fish are deprived of oxygen they will gravitate to the top of the tank to try and utilise the oxygen being created by the surface water movement. Potentially, the remaining oxygen in the aquarium will gravitate to the water surface too.
4. Fish lethargy
Oxygen deprivation requires that the fish conserve their energy, and if the matter worsens they lose energy too. They become far less active.
In fact those fish which are not normally active, like Shrimp Gobies, which remain in one spot are very likely to die the soonest. The reason for this is they rely solely on the water passing them while they sit at the bottom of the aquarium.
How is Oxygen Added to an Aquarium?
In a saltwater tank, the two main methods of oxygen introduction are as follows:
1. Protein Skimmer
Not only does a protein skimmer remove unwanted proteins/waste from your water column, a skimmer rated to your water volume is without doubt the most effective method of boosting the oxygen levels in your tank. As water passes through a skimmer it is infused with oxygen created by the venturi valve pulling air into the column reactor.
This injection of air ensures your livestock have a continuous feed of life giving oxygen at all times.
A note on new tanks – Protein Skimmers need to settle in when introduced to a new tank. Typically the skimmer creates an overabundance of bubbles that will quickly fill the cup and overflow. This can take a number of weeks to calm down.
It is very important while in this period you do NOT turn your skimmer off. Immature tanks require this vital boost of oxygen to not only for your livestock but also for the bacteria which take care of your nitrogen cycle.
A consideration with skimmers being indoors is that they can only introduce air which is circulating in the confines of the house or building in which they are situated. Some Reefers go to the extent of running a line from the skimmer intake to outside. The benefit is an increase of oxygen (compared to indoor air), which in turn means happier inhabitants.
2. Water Surface Movement
To a lesser degree, the movement of your aquariums water surface created by gyres or powerheads can also introduce oxygen into your tank. However you should not solely rely on this means of introduction.
Oxygen deprivation caused by power outage
Should electricity fail in your neighbourhood and you do not have a back of battery system or generator, the most effective way in which to ensure that your fish are not oxygen deprived is to scoop up and pour the water back into your tank creating as many bubbles as possible. Ideally this should be done as often as you can manage.
In a situation like this an advantageous tool would be an oxygen test kit to monitor the levels.
Can fish symptoms be reversed?
Identifying the above signs quickly will ensure that you can indeed reverse them.
Simply adding a skimmer will immediately start to add a massive boost of oxygen back into the water.
Should you have another unaffected tank you can place them in, your fish would recuperate in a couple of hours.