Once white spot has broken out in a system all the susceptible fish will have the parasite and, even if they have no signs, all the fish in that system will need treating. Otherwise, on re-introduction of the most susceptible species, the parasite will breakout again from the asymptomatic carrier fish that have remained in the main tank.
Treatments for marine white spot generally fall into three categories: chemical, environmental and unproven.
There is insufficient time and space to discuss the unproved group here but suffice to say this covers garlic, tea tree oil and the whole grey literature area of white spot cures.
By far the most effective white spot cures are copper based and prescription drugs such as fuscidic acid and quinine.
However, the following words of warning should be heeded before chemical treatment of a reef tank is attempted. (Source: Simon Garratt, posted on UltimateReef)
“Modern reef keeping methods have now moved way beyond the days when LR was considered a simple source of bacteria, and filtration. In modern systems the 'critter' population regularly feature as a major player in the functioning of the tank. As such, any treatment should consider the impact it will have on the tanks ecosystem.
'Reef safe' chemicals have often only been tested with the most commonly kept 'show' inverts. Many have not been tested nor claim to be safe with the multitude of background life that 'modern' reef keeping deems as beneficial, and form a substantial part of a modern reef eco-system, especially those containing sand beds etc. The use of 'chemicals' designed to kill parasites can have disastrous consequences in more diverse systems as they will kill off these beneficial animals as well as the parasite.
As a rule of thumb Keep chemicals out of the reeftank and carry out any treatments in a specialised quarantine tank. Whilst it’s perfectly acceptable and correct to deem the survival of the fish as a priority, it shouldn’t be at the detriment of the rest of the system, and certainly not to the degree it jeopardises the systems stability.”
That said, copper based treatments are easy to use and readily available from LFS in either ionic or chelated forms (chelated forms have a longer ½ life in the aquarium, otherwise there is no difference between them as the active ingredient, Copper ions, is the same). The two important things to remember about copper are that it will kill all invertebrates and cannot be used in a reef tank and that you must get the dose right. If the dose is too low then the treatment will be ineffective, too high and you will poison your fish. So I recommend that all copper treatments are carried out in a quarantine tank away from your invertebrates and that the levels of copper are monitored daily with a copper test kit to make sure the dose of copper falls into the therapeutic range of 0.2-0.3ppm. Once a tank has been treated with copper it can be problematic reintroducing invertebrates back as copper forms complexes with carbonates in the aquarium and these can leach back into the water with time causing copper toxicity to the invertebrates.
Fuscidic acid and quinine can be used in reef tanks (although ideally they should be used in a quarantine tank situation) as they are relatively safe for invertebrates, although quinine is not tolerated well by clams and anemones. However, it may be easier to remove these animals from a reef rather than catching all the fish if the need arises. These two drugs can also be used on fish species that are intolerant of copper such as sharks and rays and some scale-less species. Both of these compounds need to be prescribed by a vet and the doses of fuscidic acid should be 5mg/l for 10 days and quinine 30mg/l for 14 days. However, fuscidic acid will kill off some filter bacterial while quinine will not. After treatment both of these compounds can be stripped out of the water with activated charcoal.
The final group of chemicals are dye based and these are very popular as they are often sold as reef safe. These dyes are designed to bind to the parasites genetic material and prevent replication. They can be very effective for some reef systems and completely ineffective for others. To some extent this can be attributed to variation in biomass (these dyes readily bind to organic materials and can be rapidly stripped out of reef system in skimmers and in systems with lots of animals in them before they have time to inhibit the parasite) and errors in calculating the system’s volume can cause the medications to seem ineffective. Often they require 2 or 3 consecutive doses to affect a cure.
Unlike freshwater white spot, marine white spot cannot be cured with a rise in temperature. This is because the thermal death point of this parasite is higher (around 32-35oC) than the reef fish we are trying to cure (and this temperature would seriously damage most corals etc). Raising the temperature simply speeds up the life cycle allowing more parasites to develop in a given time period. For example at 25oC a tomite completes its part of the life cycle in 6.5 days (fig 1) at 20oC it would take 9.75 days, giving you much more time to intervene before the infection becomes “nuclear”.
Freshwater baths are ineffective against marine white spot as the parasite is embedded in the host’s skin (figure 3) rather than on the hosts’ skin. Here the parasite is protected from the external environment and freshwater cannot damage it.
Hyposalinity treatment can be a useful strategy in systems where it is impossible to get the fish out and treat them by a chemical method. You drop the SG in the tank to below 1.017 (some say as low as 1.009 but IMHE 1.015 is about as far as I would take it) in small steps around 0.002-0.003 units per day. The infectious stages of marine white spot, the tomites, can't survive the low salinity and die off. It can take a long time to cure a tank like this, at least 4 to 6 weeks often 12-16. In addition this treatment is very stressful for shrimps and urchins/starfish/brittlestars and some fish species that are sternihaline and do not osmoregulate well at low salinities.
It also plays havoc with your water chemistry and we make no apologies for repeating a comment Simon Garratt made concerning hyposalinity and the changes it causes to dKH and pH in a post on UltimateReef some time ago.
“Hyposalinity treatment is not a good idea in a modern reef tank using the Berlin method. It has drastic effects on dKH and pH stability.
At a dKH of 4, your pH becomes very unstable over a 24hr period with large dips at night, even more so in immature systems that commonly has higher degrees of algae present than older more mature and heavily grazed systems. Whilst severely detrimental to corals (especially hard corals) these levels can also cause a multitude of other problems as well.
Low pH levels are dangerous to all crustaceans especially during moulting which usually happens at night, this isn’t just your shrimps, it’s also your entire population of critter life in the tank that comes under this group, including copepods etc.
It also plays havoc with sand layers and the LR, causing big shifts in boundary layer function, possible dissolution of bound phosphates, and an overall destabilising of the entire nutrient cycling abilities of the tank.”