A friend on another board suggested I have a look so I thought I would jot down a few comment/observations for everyone’s benefit.
1. Target dose rate for chloroquine phosphate usually ranges from 10-40 mg/L, nominal (i.e. the dose that is calculated – but may not be the actual dose). Unfortunately there is some confusion in the literature. I would suggest you target 20 mg/L since your using a treatment tank with minimal things to take up space and put your volume estimate off.
2. The dose rate is based on the active ingredient – not the weight of the table. So if the package says each tablet contains 155 mg active ingredient that is what you would use for calculations. The rest of the tablet is comprised of binders and other such non-medicinal ingredients (unless it contains something else).
3. What is the volume of your treatment tank? If, for example, it's 30 gal; to achieve a dose rate of 20 mg/L, you would need around 15 tablets. That is 30 gal = 113 L x 20 (mg/L) = 2,260 mg /155 mg/tablet = 14.5 or 15 tablets.
4. Tablets should be ground up and added to a small volume of tank water to get them into solution. If you notice it is not going in, you can a little alcohol to see if this helps.
5. Treatments are usually 10 days. The usual suggestion is to treat you water for 5 days at the target dose and then do a 50% water change with make-up water at the correct dose rate.
6. With all treatment of this nature it is important to keep an eye on your fish in case they react negatively – although it sounds like they are far enough gone that there is probably not much (or much else) you can do.
7. Lastly, chloroquine is known to be toxic to invertebrates – how much is hard to say as this will depend on many variables. Just something to keep in mind. Since your fish are in a treatment tank I’m not sure why you don’t just treat with copper – which is effective against velvet and, as a bonus, you can monitor the actual treatment concentration.
As you’ve realized, a treatment tank is great idea – but a big problem if you don’t have a system running in the background that is fully cycled. If you have to set up a treatment tank to deal with an emergency the only way you can manage water quality is with a lot of water changes which presents a problem maintaining the treatment dose.
Good luck with it.
Hope this helps.
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