Water Changes in Lobster Tanks
Recirculating lobster holding systems reuse seawater, but that doesn’t mean the same water can stay in the tank indefinitely. Regular water changes are an important part of maintaining good water quality, controlling nitrate and creating a healthy environment for live lobsters.
Why do lobster tanks need water changes?
Lobsters produce ammonia as a waste product. In a properly matured biological filtration system, nitrifying bacteria convert this ammonia first into nitrite and then into nitrate.
In the natural marine environment, nitrate is taken up by algae, seaweed and other organisms. A lobster holding tank doesn’t usually have this natural nutrient cycle, so nitrate gradually accumulates in the recirculating seawater. Water changes remove some of this nitrate and other accumulated waste and replace the old water with fresh seawater.
Should you change the water if ammonia is high?
Yes. If ammonia levels in a lobster tank are too high, a water change should be carried out. Ammonia is toxic to shellfish and high concentrations can affect the health and survival of your stock.
The size of the water change should reflect how serious the water quality problem is. If ammonia is only slightly above the normal safe level, a 20–25% water change may be sufficient. If your test results show dangerously high ammonia levels, a much larger or even 100% emergency water change may be necessary.
A water change treats the immediate problem, but it is also important to establish why the ammonia has risen. High stocking levels, overfeeding, dead or weak animals, insufficient biological filtration or a biofilter that has not fully matured can all contribute to poor water quality.
When should you change the water in a lobster tank?
Rising nitrate is one of the useful indicators that a water change is due. Unlike ammonia and nitrite, nitrate is considerably less toxic to lobsters, but increasing levels tell you that waste products are accumulating within the recirculating system.
Regular water testing is therefore much more useful than simply changing the water according to a fixed calendar. Test ammonia, nitrite, nitrate and the other important water parameters and use the results to understand what is happening inside your system.
As nitrate builds towards higher levels — around 100 mg/L and above — we would start considering a water change rather than allowing it to continue accumulating. The condition of the stock and the other water-quality parameters should always be considered alongside an individual nitrate reading.
How often does a Lobster Pod need a water change?
During our original scientific trials for the Lobster Pod, we found that a water change of around 20% every four to six weeks was sufficient under normal operating conditions.
That assumes, however, that the other water parameters are correct, healthy and strong lobsters are being introduced to the tank, stocking levels are appropriate and the Lobster Pod operating guidelines are being followed.
Every lobster holding operation is slightly different. Stocking levels, how frequently lobsters are added and removed, seawater quality and temperature can all influence how quickly water quality changes.
Are more frequent water changes better for lobsters?
Generally, fresh, good-quality seawater is beneficial. If you have easy access to clean natural seawater and carrying out a water change is straightforward, there is no need to wait until there is a problem.
Regular partial water changes help remove accumulated waste and keep the water in good condition. For businesses where seawater is difficult or expensive to obtain, an efficient recirculating lobster tank reduces the amount of replacement seawater required while still maintaining good water quality.
This is one of the reasons we recommend regular testing. Rather than changing large volumes of water unnecessarily, you can see how your system is performing and make informed decisions about when a water change is needed.
Should you keep replacement seawater ready?
We think it is always a good idea to have enough suitable seawater available to carry out an emergency water change.
If you collect natural seawater, having some in reserve means you aren’t completely reliant on tides, weather or access to your collection point if you suddenly discover a water-quality problem.
If you make artificial seawater using tap water and marine salt, prepare it at least 24 hours before you intend to add it to the lobster tank. Make sure it is properly mixed and suitable for your system before use.
Having replacement water ready means that if an ammonia test suddenly gives you a result you don’t like, you can act immediately rather than having to wait.
Good water quality protects your lobster stock
Water changes are only one part of managing a lobster holding system. Good biological filtration, sensible stocking levels, regular maintenance, healthy incoming stock and routine water testing all work together.
We’ve been designing and manufacturing shellfish holding systems since 1998, and one thing hasn’t changed: looking after the water is one of the most important things you can do to look after your shellfish.
A well-run recirculating lobster tank shouldn’t need constant large water changes. Test regularly, understand what the results are telling you and change the water when the system needs it.
