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Discussion Starter · #1 · (Edited)
This isn’t a specifically “natural tank” issue, but I figured asking in a regular fish forum would result in people saying that my tank isn’t cycled because I don’t have nitrates, so figured I’d ask here to skip over explaining that part of things.

I think I accidentally gave my tetras pH shock and am wondering if there’s anything else I can be doing to help them ...

I’ve got a 32gal natural planted tank that’s been set up for about five months. pH usually hangs around 7.8-8.0, GH and KH are usually in the 8-9 area. The tank is home to two Platty’s, 9 neon tetras, 7 lemon tetras, 6 glowlight tetras, a handful of shrimp, and a healthy population of ramshorn snails. All residents have been in the tank since somewhere between October and December.

I’ve had some hydra in my tank since about Christmas (discovered when I started feeding some live foods to the tetras), and I left it for a while, hoping it would die back if I didn’t do live foods. I’d read the hydra post here, though, about treatment for it and did get fenbendazole from my vet in case I ended up needing to treat it. Finally broke down and treated the tank earlier this week (0.1g of fenbendazole per 10gal).

Fish, shrimp and snails all did fine with the treatment, and yesterday I did about a 60% water change to clear the med from the tank. Water parameters pre-water change were pH 8.2, ammonia 0.25 (which my tanks seem to always have), nitrites and nitrates both 0.

I didn’t test all of the parameters post water change as I’ve never had any issues with it - our municipal water is a steady pH of 8.4, and I use a blend of that and bottled / demineralized water so that my GH and KH aren’t through the roof.

I did, however, check my GH after the change, since that directly impacts the shrimp - it was 11, which I wasn’t thrilled with and figured I’d added too much town water.

And now the trouble starts.

This morning I found one neon tetra dead, tangled in a patch of moss. Wondered if he’d maybe gotten stuck somehow etc etc. The lemon tetras didn’t eat this morning, which was odd, but I didn’t think too much of it all.

By late afternoon, two of the lemon tetras were looking bad (like close to gone) and the others were looking twitchy. Platty’s were their normal selves, glowlights pretty normal, neons not as bad as the lemons, but not great. Shrimp and snails all good.

So. Pulled the two ill lemons out of the tank into a separate container. Checked water parameters and found that the pH was down to 7.4 (so a drop of 0.8 compared to pre-water change). Reading online, symptoms seem consistent with pH shock.

I added 4tsp of baking Soda to try to raise the pH, and that has worked - pH was 8.0 about two hours after adding it. I also added a bit more water conditioner / scale protector to the tank as a faint hope it would help.

It’s now almost five hours since I added the bicarbonate. The two lemons who were looking bad have since passed away. The other fish are continuing about as they were, with one lemon now listing slightly off kilter and a couple of neons looking dicey.

I’ve checked our town water again, and to my surprise, the pH is down at 7.4. GH 21, KH 22 .... how the pH can be that low with that much bicarbonate in it, I have no idea. Ammonia 0.25-0.5, nitrites and nitrates both 0.

So. I don’t know what else I should be doing. Or if there’s anything else. My other two tanks both run at a stable 7.4 for their pH (they were set up with mostly bottled water with Salty Shrimp added for mineralization), so I don’t feel like moving fish over to those tanks would help ... that would just toss them around the pH drop again.

The low (for us) pH of the town water with GH and KH so high makes me wonder if there’s something wrong in the water I can’t see by testing, so I wondered about doing a partial water change with just bottled water - but the bottled water with Salty Shrimp added tests at 7.2-7.4 pH, so I worry that would just make matters worse.

Have I done about all I can do and just need to wait and see how many recover? Or is there something else I can try?

Feeling horrible.

As an aside, my two 10 gal tanks both had hydra as well (plant sharing from the big tank, I think). They were also tested with the same concentration of fenbendazole (and same timing). They also had water changes performed yesterday with the same mixture of town and bottled water. Residents all doing fine, including five black neon tetras and a corydora in one of them.

Thanks.
 

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Sad story. I see two possibilities.

First, a big water change can always cause problems, especially if you use city water. For example, city of Raleigh uses chloramines to treat water and the chloramine dose varies. In addition, the city flushes the system every April with chlorine. All these changes sometimes catch a lot of local fishkeepers off-guard, resulting in sudden fish kills after big water changes.

Second, the Fenbendazole treatment would kill harmless nematodes as well as the hydra, especially in a rich soil-containing substrate or a clogged-up filter. Their death could release a lot of "death toxins" into the water. Once critters start dying, their death kills other critters. The Fenbendazole might have started a substrate or a filter "meltdown." This would explain the huge increase in GH you saw but a lower pH. (The sudden decomposition of fresh organic matter (dead nematodes, bacteria, etc) would cause a pH decrease.)

Possibly, the 10 gals had less debris in them, so the effect was not as great.

My advice: Find out what's going on with your city's water treatment. And be careful when treating with drugs. Clean the filter and remove any accumulated mulm beforehand. I would move the remaining fish into the 10 gals and hope for the best. (I doubt that "pH shock" caused your problems.)

Hope this helps.
 

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Discussion Starter · #3 ·
Thanks very much for your advice, Diana. As you suggested, I’ve moved the fish out to the smaller tanks. Sadly, another three fish didn’t make it through that process, but the rest are holding their own for now. Fingers crossed that they’re able to recover.

Because the town water does seem to be different than usual (lower pH etc), and with your thought about flushing of lines in the spring, I decided to also do a smaller water change on the bigger tank - just using demineralized water with Salty Shrimp added to it ... figured I might as well try to clear out any toxins that might be in there from organism die-off or the town water, whichever it was that caused things to tip so badly.

From the articles that were in the hydra post (Charles Harrison and Planet Inverts) it had sounded like fenbendazole at the low concentration was relatively safe - with the disclaimer that medications always carry some risks. Is it likely that I’ve done any lasting harm to the ecosystem in the tank?

I feel like, if hydra gets back into my tanks at some point, I’m not going to want to treat it. I hate that my fish have suffered as a result of either that treatment or something in the water.
 

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I'm glad you were able to salvage some fish.

I learned to accept hydra as part of a natural ecosystem. They are there in small numbers in my 8 tanks. They did overwhelm my tanks many years ago when I just dumped live brine shrimp into the tanks willy-nilly. Now, I feed my baby guppies much less, maybe 1/4th of what I used to. The fish can scrounge for the nauplii. I've not had a problem since.

If I see a hydra population growing on the glass, I take action immediately before they get out of hand. That's the trick.

You can kill adult hydra in planted tank by raising temperature to 105F for 30 min. Heat treatment will kill fish, but not the plants. Heat treatment does not kill hydra eggs, so they will come back in a few weeks--but in reduced numbers.

As long as plants are okay, I think your tanks will recover fine. No lasting damage....
 

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Discussion Starter · #6 ·
I have Platty’s and thought maybe they’d be close enough to Molly’s that they’d nibble on it, but no such luck. Or, not that I ever noticed.

Anyways, I’ve learned my lesson and will not medicate in future. I didn’t have tons, but wanted to be able to feed “real” food without worrying about the hydra getting worse.

In the end if it all, some combination of the treatment or the water change essentially decimated that tank. Tetras in another tank are all fine and happy, but I only have three tetras left from the bigger tank. It’s been a pretty awful week.
 
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