How much medicine do I need to give my fish tank?

March 27, 2008 1:12 AM

Any fishkeepers able to give me a definitive answer to how much formalin I need to put in my fish tank to try and cure a case of white spot (Ich)?

I have a small fish tank (biorb) that holds 30 litres. I recently bought some new fish but noticed white spot on one of them and borrowed some formalin from my mother. Unfortunately there aren't any instructions with it. I looked on various websites but I keep seeing various ranges and dont want to kill my fish!

The formalin I have is "pure" i.e. it is 37% formaldehyde mixed with methanol and doesnt have any other ingredients with it.

The fish are 6 small platys in a tropical set up.

posted by aqueousdan to pets & animals (7 answers total)

In the past I've used a proprietary white spot, which I think does contain formalin, and had to be added at 1 drop per gallon. The proprietary remedies aren't expensive, and have always been effective for me. I think that would be a safer bet than trying to guesstimate how much neat formalin you need. Alternatively lots of online sources seem to recommend increasing the water temperature slightly, and adding aquarium salt.
posted by roofus at 2:14 AM on March 27, 2008

All my books talk about 37% formaldahyde solution as the standard strength, and suggest 5mL per 340L (what that is in US imperial units I don't know).

When I was keeping both freshwater and marine fish, there was plenty of argument as to whether any of the standard cures - formaline, malachite green, etc - were worthwhile at all. Success rates using cures were considered to be pretty much the same as success rates with good husbandry.

At the very least, understand the life of the parasite - it has a life cycle of 15~20 days (depending on temp), and is only susceptible to treatments for about 2 days of that (just before it infects the fish and causes the actual white spots - or about 2~3 weeks after the last white spots have disappeared from the fish). Don't stop just because the fish look parasite-free; you've still got a long way to go...

Oh, and all the usual things apply - remove any chemical (carbon, resin) and biological filtration, use mechanical filtration only, isolate non-affected fish, etc, etc.
posted by Pinback at 2:29 AM on March 27, 2008

Drop the temp in the tank a few degrees and reduce the amount of light- and do daily 1/4 water changes. You can clear up whitespot without resorting to chemicals.
posted by mattoxic at 3:57 AM on March 27, 2008

mattoxic: drop the temp? that will prolong the life of the Ich. (but will slow down it's breeding rate)

I've always just raised the tank temp and added nice helping of aquarium salt. then the next day I keep raising the temp one degree, add one tablespoon of aquarium salt, then one more degree, one more dose of salt. don't raise the temp above 86F.

the increased temp will speed the life cycle of the mature breeding ich, and the salt will kill the young before they can mature.

Platys are pretty sturdy fish and handle a high salinity, but it has to be added gradually.

once the Ich is gone for a few days, lower the temp back down gradually over a few days and do daily 20% water changes to reduce the salinity.
posted by jrishel at 7:40 AM on March 27, 2008

oh, and if you have one or two of the fish with Ich that appears much worse than the others, you can give them a salt bath. just a few minutes in higher concentrate than the rest of the tank. it will shock the Ich much more than the fish and give the fish a head start on kicking the infection.
posted by jrishel at 7:42 AM on March 27, 2008

I guess I wasn't clear that the formalin is packaged as a fish disease cure. This one just seems to be aimed towards koi in large ponds instead of being diluted for the smaller tanks. I guess thats why I cannot seem to find how much to give a small tank.

Using your suggestion Pinback I think i need 0.44ml but as for measuring that out i really am not sure once again :0)

I was sure you had to raise the temperature and yeah I had looked up the life cycle of the ich realising that it is only susceptible to attack at a couple of the stages.

I wasn't so sure about the salt bath, it seems an odd idea to shock the poor fish after it has just been shocked big time by taking it in a small bag in the car to its new home. I didnt want to finish it off...
posted by aqueousdan at 1:47 PM on March 27, 2008

Well, 0.44 mL is really not going to be easy to measure out - what you want to do, if you're going to medicate, is dilute the medication by 10 x, then use 10 x the dose - if you've got an eyedropper, 4.4 mL shouldn't be too difficult.

So, depending on how precise your measuring unit is, use method A or B:

A) take 1 mL of the medication. Add 9 mL of (dechlorinated) water, mix. Dose fish with 4.4 mL.

B) take 1 teaspoon of the medication. Add 9 teaspoons of water, mix. You have more dilute medication than in A, but it should be the same concentration. Dose fish with 4.4 mL.

Does that make sense?

I had to dose my poor betta fish with levimasole once, which is only sold in the United States for pigs and sheep, so I have some experience in finangling large doses into small doses. :) However, I'm still pretty new to the hobby and have never had to deal with ich, so I would defer to the others in terms of whether or not to use the medication at all. This is just so you know how to, if you decide to do so.
posted by bettafish at 7:40 AM on March 28, 2008