A general guide to Hyposalinity

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Nov 8, 2006
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A general guide to Hyposalinity

The Ich paracite

When treating for marine ich, Hyposalinity works by breaking up the life cycle of this parasite, coupled together with the lower level of SG which will effectively reduce the level of stress on the fish.

The Ich parasite, which is really just a protozoan, goes through a number of stages in it's life span out in the natural habitat of the ocean. The start of Ich is where this gets into the fish’s skin and gills and will form a hard covering over itself as protection. It then starts to slowly feed on the tissue of the fish. What it's doing at this stage of it's life is growing inside a cyst until it has matured enough to break free from the cyst and enter the "free swimming" stage of it's life cycle. At this stage, it needs to be able to find a host in order for it to survive. While ich is in the free swimming stage, it attaches itself to areas such as the live rock, which that makes up the reef backbone as well as the substrate. This is where it reproduces. It will typically take about 2 weeks to move from infecting one fish to infecting another. The process can be increased time-wise by lowering the SG. This basically makes the cysts pop and will kill the growing parasite.

The three separate stages the Ich parasite

1)Trophont Phase: This is where the parasite gets into the fish itself and forms the hard cyst cover, which is what the aquarist will see as the actual white spot on the fish.
2)Tomont Phase: This is where the cyst breaks through the skin of the fish and will leave the fish’s body and land in the aquarium in places like the live rock and sand and will self develop itself.
3)Theront Stage: This is where the tomont will break apart and release theronts into the water column and is effectively at the free swimming stage where it can attach itself to other fish and the infection process will start again.

Where does Ich come from?

Despite popular belief, the Ich parasite does not just appear in an aquarium, it has to be added. The main method of transportation is achieved by fish, live sand and live rock. Fish can actually carry the Ich parasite without actually being a diseased fish themselves and the parasite will then fall into the aquarium and fish with a low immune system will then get infected.

What exactly is Hyposalinity?

On a basic level, Hyposalinity is where we effectively lower the specific gravity of the aquarium water to a level below natural ocean water. To make this treatment effective, the SG needs to be down to 1.009 with the tank running at its usual temperature of around 79f. Rather than using SG to set the level, you can choose to measure the water by salinity. If the latter is the case, then the salinity needs to be lowered to around 12%. For reference purposes, the average SG of natural ocean water is 1.025 with a salinity of about 35%.

What is the best place to treat Ich?

The best place to treat this parasite is by using a Quarantine Tank (QT) or a designated hospital tank. Treating Ich in the main display tank can have drastic effects on the rock and inverts, and will ultimately cause death to the inverts and remove all growing life from the live rock rendering the tank dead. The exception to the above is for people who are running a fish only tank where live rock and inverts are not used.

In general, it is best to treat all the fish you have in the tank if you spot a fish that has Ich. The reason for this is because the Ich parasite could have already infected other fish in the tank and just not be showing as the white spot at that point in time. Infection of other fish is about two weeks after reaching the free swimming stage.

Setting up the QT tank.

Forward planning in case of an Ich outbreak is always a good idea. Keeping a 10 or 20 gallon tank stored away, a heater for the size of tank, some pieces of UPVC plastic pipe work for hiding places and a canister filter rated for the tank. The filter media should be kept somewhere inside the main display tank to enable the media to be colonized with bacteria. By using the bacteria laden filter media and tank water from the display tank, you have an instantly cycled QT tank to transfer the fish over too without the need to acclimatize as it will match the same water parameters as the main display tank. When setting up the QT tank, ensure it’s clean to start with and transfer the water from the main tank. After letting the heater adjust to the temp of the tank (usually in 30 minutes), switch on the heater, add the bacteria laden filter media and filter to the tank to circulate. When the correct temp is achieved and the SG has been checked it is now ready to house fish.


The treatment needed is achieved by lowering the SG / salinity very slowly so shock is not introduced to the fish. This lowering should be quite precise and only really carried out using a refractometer. Hydrometers are not really specific enough and the swing arm variety is very inaccurate.

Once the water is down to around 1.009 SG (12% salinity), actual treatment is to keep watching the fish until the white spot has gone, then monitor for about a 4 week period, which is going to be around, on average, 6 – 7 weeks in QT. The lowering of the salinity must be done gradually over a period of days because if the drop is too severe, this will have a detrimental effect on the fish in quarantine. It is best to get the salinity lowered down to about 1.009 over a period of 2 days.

Take a measurement to ensure your salinity is in the region of 35% (about 1.025). Replace about a fifth of the water every 12 hours so that over a two day lowering period, you should end up with the targeted salinity. It is best to use aerated RO water for this, and NOT saltwater for obvious reasons.
Once the treatment starts, a very close eye needs to be kept on your salinity and top of the tank as required. It may help to mark the QT tank with a permanent marker of where the water level is to start with This will give a guide as to the level to keep topped off, which will ensure salinity does not sway too much.

The monitoring of the Ich should continue until all traces of the spot are gone from ALL inhabitants. Once treatment has finished, reverse the salinity back up to normal display tank over a period of a few days, to eliminate shock to the fish.

As a guide, the whole quarantine process is around 8 weeks which is a good fallow period for the display tank for all traces of the Ich to die off.
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