Sudden Loss Of All The Fish In A Mature Tank?

FishForums.net Pet of the Month
🐶 POTM Poll is Open! 🦎 Click here to Vote! 🐰

filterman

New Member
Joined
Sep 28, 2010
Messages
18
Reaction score
0
I've been keeping and breeding a wide variety tropical fish for almost 30 years and I still have one of my first fish! One of my aquariums is an Aqua One with its generously-sized external filter as supplied. It's been running for 4 years now with regular maintenance and an established piece of bog wood complete with Java Moss, some rocks and a fine layer of river sand sprinkled with coral sand to act as a pH buffer. About a month ago, I added a tall plastic aquarium plant with a gravel/resin base, and on 12 Sept, did my usual 50% fully treated, slow water change. As my tank is slightly understocked but with small traces of algae, on the 19/9/10, I bought 3 small Bristlenose Catfish and added them to the tank with one dose of Myxazin as a general precaution. They immediately started removing the Algae traces, so a few days later I added a few small cucumber slices. About 1 week later, I noticed most fish were spending most of their time in the top water layer but they did not look distressed and were feeding. On switching the tanks lights on the next morning, however, all the fish apart from the Bristlenose Catfish were dead (6 adult Australian Rainbow Fish and 2 Clown loaches). All 3 Bristlenose Catfish looked ok then but despite removing the dead fish, the catfish also died a few hours later. All the fish were stiff but had no obvious symptoms and were in full colour, though the catfish had slighter more mucous than you would expect from recently dead fish. On checking my water, it appeared very clear and normal with no surface films, temp 75 deg F, pH 6.8, zero Nitrite and 10 mg/L Nitrate. I've beem monitoring my heater for the past few days and it's controlling as normal. If I had a Nitrite peak it must have disappeared very quickly but the catfish could have been carrying a nasty disease, the cucumber could contain pesticides on the skin, and I can't rule out the plastic plant which might have toxic epoxy residues in the base or even my public water supply. Has anyone lost all their mature fish in a mature tank as suddenly as this? It could have been Nitrite or a faulty heater but I'm thinking of stripping the tank down and maturing it from scratch to eliminate any nasty diseases or toxins.
 
You say you added Myxazin, how much? Myxazin if even slighly overdosed can wipe out bacteria in the filter, have you/did you check your ammonia levels? Also adding meds can reduce the oxygen in the water, you say the fish were hanging around the surface, could have been lack of o2. There is also a chance that adding the BN's they could have bought in a disease, which they passed on to the other fish.
 
Although a week seems like a long time...it sounds like it was the Myxazin knocking out your bacteria, but because of the plants it took a while for the lack of good bacteria to effect the water stats enough to visibly harm the fish...did you test for ammonia?

It sounds like they were suffering from slight nitrite toxicity when they were up at the top the night before they died. Nitrite impedes the uptake of oxygen in the fishes gills, so naturally they swim to the surface where there is more oxygen to compensate. When you turned the lights off, the moss and algae stopped photosynthesising and oxygen levels were reduced, also the moss and algae would probably start up-taking ammonia and nitrite at least more slowly, possibly not at all.

So the fish are already suffering from nitrite toxicity, then there's even less oxygen and even more nitrite (and possibly ammonia). Even if just one fish was weaker than the rest and died, this would lead to an ammonia spike. Ammonia is even more toxic than nitrite to fish, and it could have a knock-on effect, every fish that dies raises the ammonia level just enough to kill another fish or all of them.

As soon as you turn the lights on, the plants would start up-taking any ammonia or nitrite int the water and the bacteria might be recovering too, so your other fish could be fine.

I would just do a couple of 50% water changes and add some carbon to the filter for 24 hours to remove any traces chemicals from the Myxazin that may be slowing down the recovery of the filter bacteria.

Its not good to add treatments to the main tank, you should use a separate quarantine/hospital tank, or not bother at all and only buy fish you know are safe (not always practical lol).
 
How many gallons is the tank.
How many fish and which type.
What the make of the test kit you are using.

Did the fish show any of these signs.
Darting, erratic swimming.
Excess mucas on body or gills.
Flicking and rubbing.
Laboured breathing, or gasping.
Swimming in circles fast, or barrel rolling.
Laying on the substrate upside down.
Fish laying upside down.
 
You say you added Myxazin, how much? Myxazin if even slighly overdosed can wipe out bacteria in the filter, have you/did you check your ammonia levels? Also adding meds can reduce the oxygen in the water, you say the fish were hanging around the surface, could have been lack of o2. There is also a chance that adding the BN's they could have bought in a disease, which they passed on to the other fish.

Hi there,
I only use Waterlife medicines and have almost 29 year's experience with Myxazin. I added one 6ml dose to 40 gallons of water with no side effects over the days that followed and Myazin does degrade. When the catfish died, I checked for nitrite and nitrate but not for ammonia due to the lower than neutral pH (6.8). I'm still suspicious of the new fish and other than poisoning, I'd be interested to hear of any diseases that might fit the bill and can wipe out a whole tank overnight. Thanks for your thoughts.
 
Although a week seems like a long time...it sounds like it was the Myxazin knocking out your bacteria, but because of the plants it took a while for the lack of good bacteria to effect the water stats enough to visibly harm the fish...did you test for ammonia?

It sounds like they were suffering from slight nitrite toxicity when they were up at the top the night before they died. Nitrite impedes the uptake of oxygen in the fishes gills, so naturally they swim to the surface where there is more oxygen to compensate. When you turned the lights off, the moss and algae stopped photosynthesising and oxygen levels were reduced, also the moss and algae would probably start up-taking ammonia and nitrite at least more slowly, possibly not at all.

So the fish are already suffering from nitrite toxicity, then there's even less oxygen and even more nitrite (and possibly ammonia). Even if just one fish was weaker than the rest and died, this would lead to an ammonia spike. Ammonia is even more toxic than nitrite to fish, and it could have a knock-on effect, every fish that dies raises the ammonia level just enough to kill another fish or all of them.

As soon as you turn the lights on, the plants would start up-taking any ammonia or nitrite int the water and the bacteria might be recovering too, so your other fish could be fine.

I would just do a couple of 50% water changes and add some carbon to the filter for 24 hours to remove any traces chemicals from the Myxazin that may be slowing down the recovery of the filter bacteria.

Its not good to add treatments to the main tank, you should use a separate quarantine/hospital tank, or not bother at all and only buy fish you know are safe (not always practical lol).

I agree with many of your points which are very relevant to this case. I have a fully operational spraybar running across most of the tank length and the Myxazin was added at the correct dosage one week before the symptoms appeared. The plants (a single 12" x 4" patch of a Java moss) could absorb some nitrate and the nitrite would only disappear quickly if my nitrite cycle was intact. As I reflect on your points and mine I'm now thinking it could be the strength of my nitrite cycle that was actually my downfall as I did find some uneaten cucumber chunks hidden behind the spraybar when fishing out the dead catfish. When monitoring other tanks in the past, I've been very surprised at just how much nitrate vegetable matter can quickly produce in a healthy tank. I did see some evidence of oxygen depletion in the morning as 2 of the catfish visited the surface for air which would explain why they were the last to die. I think that night and the previous morning, my nitrite cycle could have been working on overdrive due to the hidden one week old cucumber chunks being digested rapidly and, as the Java moss was thriving, the C02 production overnight would have reduced oxygen levels which may also have temporarily reversed the nitrite cycle for a spell. By the time I checked the water, it was all back to normal but even the catfish could not cope with the high biological oxygen demand from the established nitrite cycle which may even have swung in both directions. I now think it's possible that my fish suffocated due to excessive biological oxygen demand though a very temporary nitrite peak is also possible. I like the idea of using the activated carbon to remove any toxins which saves me stripping down the tank. As regards the remaining risk of pathogens, maybe I should try some cheap fish before opting for a full strip down. Your points have been most helpful and I'm now sold on the benefits of talking through a problem. I'll keep the tank going for now towards reaching a final conclusion.
 
How many gallons is the tank.
How many fish and which type.
What the make of the test kit you are using.

Did the fish show any of these signs.
Darting, erratic swimming.
Excess mucas on body or gills.
Flicking and rubbing.
Laboured breathing, or gasping.
Swimming in circles fast, or barrel rolling.
Laying on the substrate upside down.
Fish laying upside down.

Hi, I have a 40 gallon tank and it contained 6 off 4" Australian Rainbow fish as website banner above plus one small and one large clown loach and 3 off 2" Bristlenose catfish. As explained in my other posts, I did see 2 catfish visit the surface for air that morning but I now think the root cause could have been hidden/decaying cucumber chunks in an otherwise healthy and very established tank. I can't rule out poisoning so I'll consider carbon filtration and I can check for latent diseases by adding some cheap fish over a few weeks avoiding strip down and subsequent new tank syndrome. I only use Waterlife products including Myxazin and Haloex and my catfish did have slightly more mucous than you would expect from recently dead fish but it was very slight and came off easily. I didn't see any of the other symptoms you listed and I'm now thinking along the lines of my last post. Thanks again for you suggestions, it's good to talk.
 
You say you use coral sand as a buffer. This isn't necessarily a bad thing, but when using a substrate material like coral sand or crushed coral, it is essential to keep a check on your hardness. If for some reason you waited a little longer than normal to perform your water change or changed too much you could have submitted your fish to hardness shock (commonly known as pH shock, but that term is inaccurate). When a buffering material is allowed to stay in the environment, it steadily raises your KH and GH. If this level gets too high and suddenly there is a drop in hardness, fish deaths can result from the change in osmotic pressure. You say slow water changes, but to acclimate fish to a different hardness, it should take place over the course of a week to avoid shocking your livestock.

Take a look at the article linked in my signature. It deals with using natural buffers to stabilize pH, but the principals may apply in this situation.
 
You say you use coral sand as a buffer. This isn't necessarily a bad thing, but when using a substrate material like coral sand or crushed coral, it is essential to keep a check on your hardness. If for some reason you waited a little longer than normal to perform your water change or changed too much you could have submitted your fish to hardness shock (commonly known as pH shock, but that term is inaccurate). When a buffering material is allowed to stay in the environment, it steadily raises your KH and GH. If this level gets too high and suddenly there is a drop in hardness, fish deaths can result from the change in osmotic pressure. You say slow water changes, but to acclimate fish to a different hardness, it should take place over the course of a week to avoid shocking your livestock.

Take a look at the article linked in my signature. It deals with using natural buffers to stabilize pH, but the principals may apply in this situation.

Hi the coral sand makes up about 5% of the substrate and I put it in about 18 months ago to prevent acidosis. I've only had to top it up it once, say about 6 months ago but I'm literally talking about a sprinkle once a year. When I say slow water changes it just means that the water is dechlorinated and at the same temperature and pH but I still leave each bucket to settle for 15 minutes before adding it to the tank and generally try not to stress the fish.
 

Most reactions

trending

Staff online

Back
Top