About 2 months ago my reef tank had an outbreak of flatworms (the one’s that is lethal to SPS). Some of the flatworms are the size of pinky nails, and some as small as rice grains. They have covered on almost all SPS in the tank. Flatworm eggs litters over the base of SPS. Tentacles retracted, colors faded, tissues bloated, and some died eventually. I have tried many chemicals, every time thinking this is the last resort, and finally I found the best solution to this problem, that is Potassium Chloride, killing flatworms by potassium poisoning. KCl is cheaper than any other medication on the market (…….and apologies to all flatworm medication makers………).
I have shared this to many aquarists in my area, and including myself, have successfully rid flatworm outbreaks, and fatality of SPS is extremely low. In many cases, the treatment yields no fatality of SPS at all.
Below is my guideline for potassium dosing, and this is useful as coral dip, as well as to be used to treat entire tank for the red bugs, flatworms and pistol shrimps.
1. As the dip (Dosage for killing red bugs and flatworms)
Mix 1 McDonald soup-spoon of KCl to one liter of seawater (need not be exact). Mix well and let dissolve. Dip the SPS or LPS in the solution for 20~30 minutes. Flatworms will die and float away from the coral. You should swirl the coral in the KCl solution to help dislodging those more stubborn ones. After the treatment, place the coral back to the tank. Please remove any crustaceans that you wish to keep before this procedure, eg. symbiotic crabs.
After treatment, healthy SPS should extend the tentacles within an hour. It is normal to observe excess mucous on the SPS, in rare cases, slight color fading. This indicates the SPS is still in good health which responds immediately to changes. However if the SPS RTN severely, it is indication that the SPS is already very weak.
2. To treat entire tank for red bugs and flatworms
Maintank dosing is best done with 3 treatments. 15 days apart between each treatment. I did only 2 treatments last time. In another word, second treatment administered 15 days after the first. This is to ensure flatworm larvae are all killed. To administer, you must acknowledge below:
a. Potassium tolerance differences
Small crustaceans generally does not tolerate more than 600ppm of potassium. At this level, the more delicate cleaner shrimp, symbiotic shrimps, camel shrimps…etc. will die slowly. If not treating your tank and you still noticed crustaceans slowly die in your tank, chances are your tank potassium level is too high. Some hermit and small hitchhiker crabs could tolerate up to 700ppm of potassium, and pistol shrimps can go higher.
I have done 2 dips at level exceeds 1500ppm. Each for 30 minutes dip at this level, amphipod, small pistol shrimps, and fireworm have all died. Just when I think I have killed all pistol shrimps too, 2 larger pistols were later discovered survived. The 2 larger pistols could have been killed, maybe, if I have dipped longer.
Fish also have limited tolerance of potassium at 600~700ppm. At 700ppm, this level is enough to kill most of the fish in the tank, or just a matter of time. There were one case where the Pomacanthus xanthometopon and Zebrasoma flavescens goes straight into shocks when I suddenly raised the main tank potassium level to 700ppm. I immediately put both into clean seawater and luckily they both survived. Every organism’s tolerance of potassium level is different, and it is difficult as hobbyist to test each specie for their tolerance level. Thus we should always net out all non-coral organisms out of the tank prior to the tank treatment.
Those that supplement potassium to the tank usually tried to maintain it at 400~500ppm. Knowing you should already have this level present in the tank, we must include them into our final concentration. For these tanks, adding 1kg of KCL per 500 liter of seawater (raising 1000ppm) would make the total concentration to 1500ppm (original 500ppm + added 1000ppm).
Those tanks that do not regularly dose potassium, I would recommend to add 1.25kg of KCl per each 500 liter of seawater, which also brings the potassium level of the tank to 1500ppm.
It is important that you should always totally dissolve KCl outside of the tank, and pour the dissolved mixture to mix with the tank. KCl powder may not dissolve completely if you simply pour the powder into the tank.
Water flow need not be turned off after dosing. The water flow actually helps dislodging the flatworm from the surfaces. Dosing should take 30 minutes (you can now sit back, and enjoy the flatworms floating up to heaven). Afterwards, drain treated water out of the system as much as possible, and replace with fresh new seawater.
c. After dosing,
Even if you think you have removed all non-coral organisms out of the tank before dosing, chances are that there will be many more still left in the tank, and have died during this process. Nutrient explosion and algae bloom usually follows immediately. Biological means of nutrient removal (hermits, herbivores) in combination with vigorous mechanical filtration are highly recommended after dosing. Most SPS experts are veterans at nutrient control and should be capable of handling this situation. SPS coloration may shifts due to availability of excess nutrient, but should return back to normal in a few weeks.
d. KCl effectiveness on flatworm eggs.
It is my personal opinion that high level of potassium should be able to kill flatworm eggs. My last experience is that after the first treatment, and second treatment follows after 15 days. Sure enough, there are still flatworms died on the second treatment, but all are less than 1mm in length, and no more than 10 of them. It is apparent that most eggs were killed in the first treatment due to high level of potassium. To be safe, I should administer a third treatment, but I was lazy, and flatworms were no where to be found after second treatment anyway.