I haven't posted here in a while, but I'm at my wit's end and very frustrated. As a teenager, I maintained multiple aquariums, all sorts of fish, and never had problems like this. That was 25 years ago, and now I can't even keep a simple goldfish alive. HELP!

I have a tall 20 gallon tank that I picked up for free from a Freecycle post, roughly 2 years ago. I thoroughly cleaned the tank, multiple times, mild soapy water, rinsed thoroughly multiple times. Same cleaning process I used all those years ago.

There are a lot of "firsts" with this new setup. I used broken slate tiles glued to the back wall of the tank as a backdrop, the first time I've ever done that. The "glue" is clear silicon, purchased at Home Depot, but according to info that I found online, safe for aquarium use. For substrate, I used play sand, washed and rinsed multiple times. Into this were planted several live plants. This was the first time I've used sand, and the first time I've had live plants. As I said, a lot of "firsts" for me, stuff I've never done before.

Initially, I had a lot of trouble getting the tank established. Water is treated with AmQuel before going into the tank, so chlorine shouldn't be a problem. I started out trying to live-cycle the tank with a goldfish - the fish died the first night in the tank. After a few more failed starts, I eventually got the cycle started, and was able to keep fish alive. All was well until three months ago.

After coming home from a 4-day trip, I found everything in the tank dead. When I left, all fish were alive, healthy, and behaving normally. Four days later, they're all dead. Ammonia level was high, but I don't know if that was a cause or an effect of the dead fish. I waited a few days for the levels to come back down, then added three new fish. They died overnight.

At this point, I decided to step back and return to the basics. I removed the sand and the live plants, thoroughly cleaning the tank again. I started over with plastic plants, and some simple aquarium gravel from the pet store. For TWO MONTHS, I monitored ammonia/nitrate/nitrite levels, "feeding" the tank with bits of food. I saw the expected ammonia spike, followed by nitrate and nitrite spikes. I watched strands of algae grow like mad. I then waited another week, testing the water daily, and after a week of clean tests, I bought fish.

Last weekend, I added three balloon mollies to the tank, along with two ghost shrimp. Everything seemed OK, the mollies were happy devouring algae, and were very active. Within three days, they had nearly cleaned the tank of all algae. Wednesday night, I sat and watched them for a while, everything seemed normal. When I got up Thursday morning, everything in the tank was dead.

I don't know what I'm doing wrong. I just tested the ammonia levels again - 0.25ppm, certainly not a lethal level. I'm frustrated, and on the verge of draining the tank and giving it away.

Any suggestions?

Weird and discouraging. I'm inclined to say some kind of poisoning, but the fish aren't dying as soon as they go in. I'd personally never use soap on anything tank related, but the dangers (it strips the slime coat off a fish) are minor and shouldn't last. Mislabelled silicone, if it's the mould inhibiting stuff, can kill fish, but I always use hardware silicone with no problems.
Is anyone around using sprays, cigarettes, etc? I had a toxic second hand tank because the previous owner had sprayed for roaches (surprise surprise) but again, by the time I found out the problem, fish weren't dying anymore. A friend had a toxic tank because of condensation from an ancient pipe overhead (unfinished basement in a 100 year old house) dripping. I'd look outside the tank.
Then again, goldfish are notorious for keeling over as they are poorly cared for by stores, shippers, farms etc. Your second die off was when you were away. The balloon mollies had a good feed of natural food, but the balloon mutation causes them to have deformed intestinal tracts -a severe handicap for digesting 'real' food.
It could be as simple as nasty coincidence...

Yep, I wouldn't clean your tank with a soapy mix again. Other than that I am sorry to hear that.

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Are you using a heater?

Yes, I guess I left that out of my story. Heater is in place, temp is held at a constant 70 degrees, as measured with a seperate submersible thermometer.

what is your acclimation process?

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I float the bags for 15 minutes, then mix in some of my own water, float for another 15 minutes, then transfer the fish using a net.

that is pretty standard practice for a lot of people, but I really recommend drip acclimating. It has very good success rates. Also if you want to continue with bag floating, I reccomend floating for about 40 min or so and adding small amounts of water every 5 min.

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75g Blackwater Oscar tank, 55g rescued Koi tank, 55g Native tank, 55g Community tank, 29g Community tank, 25g Bolivian Ram tank, 20H GBR tank, 20L Black Convict, 20L in progress, 10g Fry tank, 10g Dragonscale betta tank, 3g Crowntail betta tank.

Heaters can get stuck on and cook the fish, but it doesn't sound like that's the problem if you have been checking the heat. I'll do my best to work through what you said and see if I can help any.
Okay soap is not usually recommended, but I use fairy liquid myself sometimes, as long as it's rinsed very well I don't think it should be a problem.

pure silicon is safe, did you check it doesn't have any additives like mold killer.

There was no time for it to be ammonia poisoning. It is quite likely the fish was already sick, it was going to die no matter what you did. Could have been caused by poor acclamation or some type of poisoning. Helpful thread on acclamation:
Drip acclimating fish.


It is not uncommon for fish to die during cycling from ammonia or nitrite poisoning. Keep ammonia and nitrites bellow 1ppm through water changes when cycling with fish.

How long had the tank been running for at this point? Had you added any fish recently? Could the tank have been overstocked or stocked too quickly, causing a crash?

Again how did you acclamate? Did you change any of the water?

It is getting strange, not quite sure what to say. It would probably be better to only add one fish to start with.

Even .25 ammonia isn't good but agree it wouldn't normally be lethal short term. It might stress fish long term and cause them to become sick (and balloon mollies are not the hardiest fish) but it doesn't explain all dying at once. Did you test right away on Thursday morning? Had you been testing regularly? Sometimes ammonia spikes drop quickly so they may have been much higher but dropped before you tested.

It's not clear to me if there have been a series of small disasters here or one big factor, or maybe a combination of the two. It seems like your original problems could be put down to cycling problems, or bad fish to start with so I would concentrate on the last two attempts.

How long was the tank running without problems? How many fish did you have at this point? A tank that is stocked to the limit (or slightly over) can be easy to crash. For example one fish may have died causing a ammonia spike that killed the rest. Or a power cut can be enough to tip the balance.

Poisoning is a possibility. Check the silicon to make sure it's 100 pure. Do you know if the tank was being used for fish before? It's always possible they used the tank for mixing chemicals or something. And there is the soap you used. I would try lots of water changes to flush out anything bad. If your tank was running fine for quite a while I don't think this was it though. As navigator black said definitely consider poisoning from outside the tank, air fresheners, furniture polish, bug spray.

Diseases like fish TB can cause long term problems but fish generally die slowly one at a time so I don't think that's it.

Lack of oxygen or CO2 poisoning can cause sudden deaths of all the fish, but I don't see why you would have a problem with that. Overcrowding, poor water circulation and high temps can cause oxygen problems. I use an air stone in the summer because low oxygen can be a problem in our hot summers. Fish gulping for air or hanging around at the top of the tank is a warning sign.

Some kind of mechanical failure: Keep an eye on the heater and make sure the filter is working properly.

To avoid problems caused by ammonia or nitrites: Generally speaking make sure the tank is properly cycled. Build up stock slowly, just add one or two fish at a time and wait a couple of weeks before adding more. Don't overstock. Make sure the filter is plenty for the size tank and fish load.

I've just said everything I could think of hoping that you might pick up on something as you read through. Let us know how it goes.

What is your tank ph right now? What is the ph of your tap and your tap 24hrs later after letting it sit out?

Good question

You know, I've never tested the pH. Not something I've ever had problems with, and never thought of checking that. I'll test it and report back.

After a bumpy start, the tank stabilized. The first fish to stay alive was a cory catfish. I then added a mystery snail and two glass catfish. The last fish added was a clown loach, added to deal with an invasion of snails who snuck in with some of my live plants.

For about 14 months, this was the entire population of the tank, and as far as I could tell, all were happy and healthy. The first week of 2012, my wife and I left for a 4-day weekend. I left one of those slow-release food tablets in the tank for the weekend.

Upon returning from that long weekend, I found everything in the tank dead. I immediately tested water, ammonia was 1ppm. I don't know if the ammonia spike killed the fish, or if the dead fish caused the ammonia spike. I'm not sure how long they had been dead before we got home.

It was this point that I decided to give up on the sand substrate and live plants, for a return to what I knew from my earlier years with fish - plastic plants and gravel. That was 2 months ago, and last week was my first attempt to add fish, after waiting for the ammonia/nitrite/nitrate spikes to occur.

I think stick with live plants, but vacation feeders are probably a no go. They must give off a lot of waste.

I always make a point of never ever allowing pet store water into my tanks. However you acclimate, the possibility of introducing disease from a chain store is huge, and seems reduced by avoiding that water.

Other than possible stray voltage from a bad heater, I don't see anything but bad luck.

I see a red flag here. I don't know much about them but I think those slow-release tablets can cause big problems. They have a calcium base so if you have low pH and water hardness it may have caused a drastic increase in pH also it could have made the water dirty. It shouldn't really be enough to kill all your fish but maybe some factors combined to crash the tank. Next time you go away for less than a week just don't feed the fish, it won't do them any harm.

I don't usually see testing of pH as important, it is not usually something to worry about, which is why I didn't even think to ask about it. Any normal pH will be fine for most fish once they are used to it. A stable pH is more important under certain circumstances (involving low water hardness and a build up of organic matter) a pH crash can occur, which can cause sudden fish deaths. A sudden pH increase because of adding something to the tank can also be a disaster. I discovered this in my youth when I decided to add a sea shell to the goldfish bowl. The goldfish actually survived but was later eaten by a cat:(. Now I know how man things are wrong with that story, but we learn as we go in this hobby.

Where do you live? Do you get well water or tap water from pipes?

The only time I've seen sudden death of an entire tank of mine is when some little kids put alka setzer in a tank. That probably doesn't apply in this case. The only thing I can think of is poor water oxygenation and/or not enough filter power.

Bingo.

IMHO

I never never use those feeding things. Most especially for a 4 day vacation. Just leave and come back.

What types of plants did you have? thriving plants should keep ammonia low regardless.

I also recommend peat moss in the substrate but for hardy fish that is not necessary.

my .02