Hatchet fish deaths in 55 gallon  11/14/08
Hi Crew--
I (and my fish) appreciate all the time and work you put into this site.
I'd like to know if any of you can answer a question I have about my 55 gallon tank. I just put it back up (was on the porch after its previous inhabitants outgrew it and moved on to a larger tank). I wanted to try an Amazon biotope, so I used "play" sand for my substrate, planted some Amazon swords, and put some wood (bought from fish store) in it. I cycled it with BioZyme and some minnows (I QT minnows for my gars, so I was fairly sure nothing icky was getting introduced to the tank). Filtration is an Aqua Clear 110 with carbon removed and extra media in its place. There's also a Coralia air circulation pump that doesn't produce a really strong current; it just ruffles some of the leaves of the plants. The tank cycled pretty quickly, in about two weeks, and after my levels all returned to zero, I purchased 18 Cardinal Tetras, 8 Swartz's Cory Cats, and 12 Marbled Hatchets. The minnows were removed right before the new fish were done acclimating and added to the tank, so I know the cycle wasn't interrupted.
I thought I was safe adding fish since the tank was cycled and the fish were all an inch or smaller --maybe this was my mistake. Since putting the fish in the tank, I have lost one Cory and five hatchets. All the fish have died at night, and we find them the next morning. My levels are:
Ammonia - 0, Nitrites - .5, Nitrates - 10, and pH - 6.5. The temperature is 78 degrees, and the light runs on a timer for twelve hours a day. I ordered my fish online, and I expected to lose one or two, but these numbers have me worried. As you can see, my levels went up slightly upon introducing the fish, but nothing has ever gotten higher than the figures I mention above, other than nitrates, which are coming down from 20. The fish never "look" sick, though my Hatchets have never really been the "top swimmers" I expected them to be. They stay more in the middle with the Tetras. I'd really appreciate your opinion on what could be going on here, so that I might save the rest of them in time. If I've missed something on the FAQ's regarding this problem, please direct me to it.
Thanks again for all you do.
--Melinda
<Hello Melinda. A few things may be relevant here. To start with, you probably didn't cycle the new tank properly: two weeks is an awfully short period of time to cycle a new aquarium. BioZyme (and indeed most every "bacteria in a bottle" product") is not nearly as effective as the marketing suggests. In the case of that particular product, my understanding is that it isn't meant to mature filters but to help with nitrate reduction. In any case, a good rule of thumb with bacteria cultures is this: if it isn't kept in a fridge and doesn't have a short shelf life, it's probably useless. Plants have no real effect on the speed at which cycling occurs, though fast growing plants (as opposed to Amazon swords) can consume ammonia directly fast enough that a well planted tank can support a small number of fish without the filter being fully mature. Next up, while the minnows will produce ammonia and are hardy enough to tolerate the cycling process, if the tank was being filtered with these fish, I'd expect cycling to take at least four weeks, perhaps six weeks. Regardless of how long cycling takes to finish, there's a danger period afterwards during which the tank is not completely stable. So delicate fish -- such as Hatchets -- should not be added to the tank for a good two or three months after cycling has finished. What you're concerned about are things like pH instability and short-term spikes in ammonia or nitrite. Since you have a nitrite level of 0.5 mg/l, I'm pretty confident that your filter hasn't completely matured and may well be in the "shaky" post-cycling phase where ammonia and nitrite levels can fluctuate. Now, the next thing I'd be worried about is pH. You mention having a low pH of 6.5, which is great for tetras and Hatchetfish, but you say nothing about hardness. One of the very common mistakes people make is to change the pH (e.g., by adding pH buffers bought from the pet store) without changing water hardness first. Be clear about this: pH doesn't matter, except insofar as it is stable. What fish care about is hardness. Marble Hatchetfish need very soft water to do well, and to be honest they're pretty finicky fish at the best of times, so if you aren't 100% sure about how to soften water and how to stabilise pH in low hardness environments, they're best avoided in favour of the much sturdier Silver Hatchetfish.
http://www.wetwebmedia.com/FWSubWebindex/fwsoftness.htm
Finally, let me make the point that your shouldn't be feeding minnows to Gar (by which I'm assuming you mean Lepisosteus). Minnows (and Goldfish) are very fatty and contain a chemical called Thiaminase that breaks down vitamin B1. So even putting aside the animal cruelty issue, it's just not a very clever way to keep your fish. Gar will eat just about anything, dead or alive. They will readily take chunky seafood. Frozen foods are good because they're safer: anything sold for human consumption will be safe for your fish. Squid is particularly good because it contains no thiaminase at all, and is not very fatty either. Crustaceans (prawns, etc.) do contain some thiaminase so should be used sparingly. My Gar loved oily fish like mackerel, but these make a complete mess of the tank, so while highly nutritious, use such fish meats sparingly and just before doing a big water change! Among the thiaminase-free white fish are flatfish and gadids (cod, pollack, etc.). If you must use live feeder fish, grow your own livebearers, and gut-load them beforehand with algae-based flake food.
These are the ONLY safe feeder fish. Goldfish, minnows and "feeder guppies" from the pet store are nothing other than parasite time bombs. Cheers, Neale.>

Re: Hatchet fish deaths in 55 gallon  11/14/08
Hi Neale--
Thanks for your reply. So, I had no fish deaths overnight. If the problem was indeed that I cycled too quickly, and not completely, hopefully this is a sign that I'm on my way. The "danger period" was something I wasn't aware of, but in the future, I'll wait longer to make sure it's passed before adding sensitive fish. I had no idea that one hatchet was hardier than another; thanks for that information. If I replace the ones I lost, I'll look into silver hatchets instead. Also, I'll look into water hardness. We have tested for it before, but not recently. It was my understanding that since that we have trouble keeping pH up in our other tanks, it meant our water is soft, but now that I'm reading about water hardness, I see that other things could cause drop in pH as well. I completely understand your concern for my feeding the gars minnows, but we've tried squid and night crawlers (which our catfish eats) and the gars aren't interested. One of them does, however, eat algae disks placed in the tank for the snails, which is fun to watch. I will continue to try to move them onto non-live food; it would eliminate the time (and tank space) I expend to QT minnows. Thanks again for all of your help.
--Melinda
<Hello Melinda. Yep, there is this indistinct phase post-cycling during which environmental conditions can vary. I'm not sure about the science, but whatever the reasons, it's best to wait a few months before adding anything delicate. Marbled Hatchets are indeed notoriously sensitive. The relationship between pH and hardness is not quite as simple as people sometimes think, which is why measuring pH (or buffering to a certain pH) isn't the same thing as changing water chemistry. By default, it's always best to go with medium hard water because this tends to buffer the pH quite well by itself (usually around 7.5) without being so hard and basic softwater fish get unhappy. Ironically, it's easier to lose fish in a softwater aquarium than in a hardwater aquarium, despite the fact most tropical fish come from softwater areas! As for feeding gars: hunger is the key! These fish can go weeks without food. My specimen, Lepisosteus oculatus (the Spotted Gar) loved Hikari Cichlid Gold pellets. These are excellent staple foods for carnivorous fish. There's really no point at all using Minnows or Goldfish because of the long-term problems the fats and thiaminase cause. This has been discussed over and over in the fishkeeping press. Bob Fenner has made the point that the #1 cause of mortality among Lionfish is the use of Goldfish as feeders. Nutritionally, Goldfish and Rosy Red Minnows are essentially the same: high-fat, high-thiaminase animals. Anyway, if predatory fish *think* they're going to get live food, they'll ignore other foods. Leave them without food a week or two, and they should eat just about anything. Cheers, Neale.>