Medication Crashed Cycle, What Next?

[Schwack]

Long story short, I ended up with camallanus worms in at least two tanks. Since my fish were no longer eating, I opted to dose twith levamisole. Per the instructions from Select Aquatics, I dosed twice over two days (25% water change + 1 dose, 25% water change + 1 dose.) I used the 15 gallon spoon for my 20 gallon long (it holds ~16.5 gallons of water after substrate, hardscape etc.) so I'm reasonably certain I didn't overdose. No inverts were impacted, and my remaining fish have been passing worms like crazy.

Since then all my tank's inhabitants have been acting normally, albeit with reduced appetites. However, since the levamisole treatment I've been able to detect ammonia in my tank. It's been cycled and running for close to a year with no issues and the only change I've made in the last several months is the application of the de-wormer. I've been monitoring it over 4 days now, and I'm consistently seeing detectable and rising ammonia levels in the water. I vacuumed the substrate thoroughly for each water change to help remove any dead worms, and to remove rotting organic matter in general. I would be very surprised if built up organics were the cause of the current ammonia spikes. The tank is very lightly stocked, thanks to the worms, but there's clearly not enough of a working bio filter to keep up. 

I've tried bringing media and filters from other cycled tanks in to help things catch up, but that's been no help. My concern is that the levamisole has wiped out my bio filter and since it's still in the water, is wiping out any new bacteria I introduce. I'm at a bit of a loss in terms of ways to remove the medication from the water. I had some carbon on hand, and I've added that to my HOB, but I'm not sure if there's more I could be doing.

Other than carbon and water changing, is there anything I can do to speed up the process of clearing the levamisole from the tank? It seems like its presence is wiping out any beneficial bacteria I introduce.

I'm also not able to find anyone whose experience with levamisole mirrors my own. Most people seem really happy with the treatment and don't experience a cycle crash.

Any thoughts on what might've caused my treatment to go haywire?

Thanks in advance for any advice! Battling these worms has had me bummed out for weeks now. I felt like I finally had the upper hand once I managed a diagnosis and treatment, but it's gone all pear-shaped on me.

[Andy's Fish Den]

I have never had to treat a tank with levamisole  "knocking on wood" so I don't know if it will kill off the bio filter, but it sure sounds like it did, or there was so many worms in the tank and the fish that it overwhelmed the bio filter that was established. But, what I would do if I was in your situation is the following: get some carbon and put in a media bag then put in a hang on back or canister filter and run, change it out every other day just so that the carbon is fresh and doesn't get depleted. Do water changes, I would do in the neighborhood of 50% every other day, making sure to vac the substrate to get any worms or other nasties that are dead. Use a beneficial bacteria booster like Fritz zyme 7 to help boost up the beneficial bacteria, adding in every time you do a water change.

[Schwack]

Yep, my first thought was that I'd released so many dead worms into the tank and the resulting decay was causing the ammonia spikes. Went through and did an extra thorough cleaning. I ended up cleaning out my intake sponge last night because it was full of what appear to be bunches of dead worms. The sponge looked like it had somehow pulled a bunch of dog hair out of the water. I was wracking my brain all day trying to figure out how dog hair had gotten in the tank. It wasn't until I threw one under the microscope that I realized they were all worms.

I've got a few pre-packaged carbon bags I can throw in the HOB. It'll probably be cheaper to grab loose media and a bag once I run out, especially if I'm swapping them every couple days. I'll keep up with the 25% daily water changes I've been doing, they seem to keep the ammonia levels down. I guess I'm just gonna be fish-in cycling these tanks for however long that takes. Yuck, I had hoped I was done with this after I had several tanks with established cycles.

[CT_]

Seems unlikely to me that Levamisole would kill bacteria.  I assume since they haven't been eating you haven't been feeding much either.  Perhaps your bacteria have cutback to very low bioload levels now and the sudden start up of feeding has increased the bioload.

[Frank]

I'm sure that you searched everywhere. But, is there any chance of there being a dead fish somewhere?

[Schwack]

51 minutes ago, CT_ said:

Seems unlikely to me that Levamisole would kill bacteria.  I assume since they haven't been eating you haven't been feeding much either.  Perhaps your bacteria have cutback to very low bioload levels now and the sudden start up of feeding has increased the bioload.

Right? I can't find anyone on the internet who has had the same experience with their biofilter being wiped out by levamisole hcl. It's a commonly used dewormer, at least for red worms, and I would expect SOMEONE else to have experienced this. I had cut back feedings to once every 3 days or so and am now back to feeding lightly once a day. I'll keep an eye on it, but I'm stumped by the steady rise in ammonia and flat levels of nitrates.

31 minutes ago, Frank said:

I'm sure that you searched everywhere. But, is there any chance of there being a dead fish somewhere?

Dead fish? Definitely not. I kept a close count on 'em. Dead shrimp was my second guess, after piles of rotting worms, since they've been breeding like little water rabbits. I've torn up every bit of hardscape in the tank in search of a stray body, but no dice.

Like I said, I'm at a total loss to explain how an anthelmintic would wipe out bacteria, but in both tanks I dosed the levamisole I have the same issue. It's blowin' my mind.

Edited February 10, 2021 by Schwack

[CT_]

46 minutes ago, Schwack said:

Right? I can't find anyone on the internet who has had the same experience with their biofilter being wiped out by levamisole hcl.

Indeed.  Also it mechanism of action is to interfere with things that bacteria don't have so it would have to be incidentally toxic to bacteria to kill them.  Most of those things are also toxic to people and fish---and life.