Tetras disappearing, please help!!

Hello everyone, it is my first time posting on a forum so please bear with me.

We have a 160L well planted tank with a Large external filter. I clean the filter every 6 months/when it needs doing. Unfortunately I don't know the speficiations of the filter as it was given to us as a gift, along with the tank. I do weekly water changes and treat my water based on the strip tests. I use Tetra EasyBalance, Microbe-lift Aqua Balance Nitrate Remover, Aquadur minerals for the GH and Aqua Care Bio Boost.

We have 5 rosy barbs, 4 clown loach, 7 rummy nose tetras, 4 congo tetras, 2 black neon tetras, 1 neon tetra. 1 ghost knife fish, 3 catfish, 2 bristlenose pleco, 1 red tailed black shark and 4 honey gouriamis. The loaches, plecos, angels and knife fish are relatively small, vary in size and aren't any bigger than 3-4 inches. The gouriamis are fully grown and most of the tetras are fully grown. I feed them 4 small cubes of frozen bloodworm twice weekly and do a mixture of flakes, mini granules and catfish pellets the rest of the week. All my fish appear to be eating well and even the knife fish loves the granules. There is plenty of hiding places for my fish with rocks, boats and tall plants.

Now my problem is that my tetras are going missing. They all vary in size, rummys, neons & congo have gone missing over a period of time. I literally bought 5 congos the other day and now I have 4 (they are relatively big in size) am I doing something wrong? Could they be jumping? Being eaten? I am at a complete loss as to what is causing my tetras to disappear without a trace. I've spent hours searching the tank and the area surrounding the tank. I would really appreciate someone's help on this as we've had the tank nearly 12 months now and I don't want to see my fish die. The guy at Maidenhead Aquatics said that the congos and gouriamis should be happy in our tank, despite us telling him about the other fish we already had.

Any advice is much appreciated. Thanks

Pictures of the fish and tank?

Filters should be cleaned at least once a month and every couple of weeks is better. Filter media/ materials should be cleaned in a bucket of tank water. Re-use the media and tip the bucket of dirty water on the garden/ lawn.

How much water do you change when you do water changes?
Do you gravel clean the substrate when you do a water change?
Do you dechlorinate the new water before adding it to the tank?

What is the ammonia, nitrite, nitrate and pH of the tank water and tap water?

The person who gave us the tank and filter suggested every 6 months. The specialist at my local pet store who specialises in tropical fish keeping also suggested the same. We cleaned it about a month ago in tank water. I do about 30% water change, I clean the gravel when I change the water and clean the filter tubing when it needs doing.

I use tap water conditioner, we don't use anything to decholorinate. I took a sample to the specialist fish keeping store who stated I didn't need to dechlorinate. Ammonia is 0. Nitrates are 100, I did a water change yesterday & added the nitrate treatment to my tank. Been having an issue with keeping the nitrates down. Tank Ph is 7.2. Tap water nitrate is 0 and PH is <6.

All other fish are healthy and I haven't had any health issues with any other fish since having the tank. My tetras don't appear to be poorly, just disappearing overnight. The guy at the store seemed to be stumped too.

I've attached a picture of my tank and filter.

knife fish will eat tetras, angels love neons as a quick treat. Clown loaches will eat tetras. Gouramis will eat tetra, depending on what cat fish you have they will eat tetras, the red tail shark wont eat them but he could kill him. You have a bunch of fish that dont belong in the same tank either compatibility or get to large.
Clown loaches can get over 16inches belong in groups which require 100 gallon tank or more. Angels belong in groups of at least 5 and require at least a 100 gallon. Congo tetras are too big and energetic to be kept with smaller tetras like rummynose neon black neon.plecos are territorial and should be kept to 1 per tank unless breeding in a species tank without any other bottom dwellers. If your catfish are corydora clown loaches and corydora arent a good mix as they occupy the same area in the tank and the loaches get far too big and active for corydora.
Congratulations though you didnt mix any hardwater fish with your softwater fish.
Keep peaceful community fish separate from big semi aggressive fish like clown loaches angels gouramis and red tail shark.
If your cat fish are raphaels or syndontis then they are definitely eating your tetras, most likely at night as they are nocturnal feeders.

If you are on mains water it does need dechlorination. No question about that.
Nitrate cannot be "treated" It needs to be removed. The only way to do this is via water changes. Try doing a 75% change every day for a week. I do a weekly 75% change on all my tanks. The problem with a 30% change is you leave 70% of the bad stuff behind and its concentration increases over time. The idea of the large water changes is you remove more in a week that was added in that week so never end up with "old tank syndrome"

Filters should be cleaned regularly because they trap fish poop and that causes the water quality to deteriorate, and it encourages harmful microscopic organisms to grow in the tank.

Basically all the water is filtered through fish poop and the water, whilst looking clear, is contaminated with micro-organisms and fish poop. Cleaning the filter regularly means the water is going to be cleaner and have less harmful microscopic life in it.

Dirty filters can also contribute to high nitrate levels. You should check your tap water for nitrates to make sure you aren't adding nitrates to the tank when you do water changes.

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You should do bigger water changes. I recommend doing a 75% water change and gravel cleaning the substrate once a week. If water is scarce then do it every 2 weeks.

You do water changes for 2 main reasons.
1) to reduce nutrients like ammonia, nitrite & nitrate.
2) to dilute disease organisms in the water.

Fish live in a soup of microscopic organisms including bacteria, fungus, viruses, protozoans, worms, flukes and various other things that make your skin crawl. Doing a big water change and gravel cleaning the substrate on a regular basis will dilute these organisms and reduce their numbers in the water, thus making it a safer and healthier environment for the fish.

If you do a 25% water change each week you leave behind 75% of the bad stuff in the water.
If you do a 50% water change each week you leave behind 50% of the bad stuff in the water.
If you do a 75% water change each week you leave behind 25% of the bad stuff in the water.

Imagine living in your house with no windows, doors, toilet, bathroom or anything. You eat and poop in the environment and have no clean air. Eventually you end up living in your own filth, which would probably be made worse by you throwing up due to the smell. You would get sick very quickly and probably die unless someone came to clean up regularly and open the place up to let in fresh air.

Fish live in their own waste. Their tank and filter is full of fish poop. The water they breath is filtered through fish poop. Cleaning filters, gravel and doing big regular water changes, removes a lot of this poop and makes the environment cleaner and healthier for the fish.

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If you are using tap water, it either contains chlorine or chloramine and you should add something to it to neutralise these chemicals so they don't poison the fish.

You can contact your water supply company via phone or website, to find out if they add chlorine or chloramine to the drinking water.

If you use well water, then you don't need to add anything to neutralise chlorine or chloramine because there shouldn't be any in the well water. However, well water should be checked each month for ammonia, nitrite, nitrate, phosphate, pH and GH.

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If your nitrate level is 100ppm, I believe your fish are dying and being eaten by the other fish. Reducing the nitrates will make a difference to the fish's health and should stop them disappearing.

We recieved 4 Angels, rummy nose tetras, catfish the black neon tetras and the neon tetra with the tank. They were all kept in the same tank before we recieved them and the previous owner never had any issues. We have consulted various pet stores and specialist with regards to our vast variety of fish who all stated they are fine to live together peacefully, we always do this before purchasing the fish. We feed them well to try and avoid them eating other fish. They don't disappear every day, maybe every couple of weeks or so.

Thank you for all your advice and I will definitely take it on board during the next water change. I put weekly nitrate remover in the tap water and the water that is left in the tank to try and keep it down.

Welcome to TFF.

I agree with other members above; your main issue is the inappropriate fish stocking and the size of the tank. The two are obviously related but the combination of species is a serious problem and would be regardless of the tank size. I realize you might think there are no problems, but there will be; the fish have inherent traits and needs that cannot be changed or ignored in time. This is something like a ticking time bomb. You may already be seeing some consequences in the disappearing fish.

As I mentioned previously, I use tap water conditioner, bio boost, easy balance and nitrate remover at every water change.

DG28 said:

We have consulted various pet stores and specialist with regards to our vast variety of fish who all stated they are fine to live together peacefully, we always do this before purchasing the fish.

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This was bad advice of the worst kind. Unfortunately, it is never good to listen to advice from fish store staff; most do not have any training/education in fish species and habitats, and some sadly only want to sell fish. It doesn't really matter, the advice here is just plain wrong, and you are going tohave serious issues which as I said above are already showing up.

DG28 said:

We feed them well to try and avoid them eating other fish.

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This is not how it works. Each species of freshwater fish has evolved over thousands of years to function within a very specific environment, which covers everything associate with the fish's life. The inherent beehaviourts normal to that species, along with their requirements, temperament, etc, are programmed into the DNA of the species. Individual fish can react to external stimuli a bit differently, but the basics for a species remain and none of us is ever going to alter them.

Maybe I need to have a word with my local specialist as he clearly isn't advising correctly and for a novice fish keeper like myself, I would just do as they suggest which is what I've been doing.

Anyway I don't know what to do with all my fish now. Due to the pandemic, we can buy fish but not return them. I will do a big clean out (water, filter etc) at the weekend as i am working round the clock until then. In the mean time I will put nitrate remover in to try and keep the fish happy.

DG28 said:

As I mentioned previously, I use tap water conditioner, bio boost, easy balance and nitrate remover at every water change.

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Water conditioner is necessary (tap water will have chlorine or chloramine). Bio boost is not necessary, though it should not cause serious problems as it is a bacterial supplement (sort of). Easy Balance is risky in any aquarium and sould not be used; the claims it makes are questionable at best, and more likely dangerous. All these additives get inside the fish, causing more trouble.

DG28 said:

Maybe I need to have a word with my local specialist as he clearly isn't advising correctly and for a novice fish keeper like myself, I would just do as they suggest which is what I've been doing.

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Don't feel bad about this, it is something that so many of us on this forum have also experienced. We learn and move ahead the wiser.

Back when I had my first tank, some 60 years ago now, there was no internet, no local books or magazines. The store person was the ony "help." When I got back into the hobby in the early 1980's I was fortunate to havee an extremely good local fish store, owned and staffed by hobbyists. That set me on the right path, but it was lucky for me I had them.

Lovely, more bad advice from pet stores. Will not be using easy balance anymore. I feel so bad & stupid about getting all of this wrong, I just want my fish to be happy & healthy. You've ust took the words out of my mouth haha.

We will get a bigger tank in the future (very costly things) to accommodate my growing fish. They are very small atm so we have a bit of time. I guess another issue is that because we didn't buy all these fish, we don't know the age of them or how healthy they are. We noticed one of the tetras had white spot/velvet disease when they came to live with us but I treated that straight away without issues and haven't seen it since.

I've spent my whole life wanting fish and now I have them I just want to do it right

DG28 said:

Lovely, more bad advice from pet stores. Will not be using easy balance anymore. I feel so bad & stupid about getting all of this wrong, I just want my fish to be happy & healthy. Just took the words out of my mouth haha.

We will get a bigger tank in the future (very costly things) to accommodate my growing fish. They are very small atm so we have a bit of time. I guess another issue is that because we didn't buy all these fish, we don't know the age of them or how healthy they are. We noticed one of the tetras had white spot/velvet disease when they came to live with us but I treated that straight away without issues and haven't seen it since.

I've spent my whole life wanting fish and now I have them I just want to do it right

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And we want that too, believe us. We care about our (and your) fish.

My recommendation would be to re-home some of the fish now, meaning as soon as you can manage it. Other hobbyists, or a local store. Not only do you have a pending large tank issue, but some of these fish cannot be together regardless.

The Black Ghost Knife fish and the angelfish could live together, they are sympatric species in some of their habitats. But the Knifefish needs a tank that is at least six feet in length by at least 2 feet in width. This fish will attain 20 inches, though usually slightly less in the aquarium. Having an inflexible body, it must always have a tank that is wider (front to back) than itself in order to turn. Smaller tanks can accomodate the fish as it grows, but the tank should always be no less than triple length and wider than the fish's length.

The Clown Loaches need a tank minimum 8 feet in length, and they should not be combined with the knifefish nor angelfish. This is a highly social fish (loaches are), and it develops an hierarchy early on when they are together. Fivee is the recommended minimum, but if you were to keep the four you have I would not add to them, and hope for the best; adding a loach or two to a group that has been together and formed its individual hierarchy rarely works.

I realize the above fish are not at maximum size yet, but they will be and not all that far down the road. Plus they are "developing" in ways we cannot see, individually and interspecies, and this requirees sufficient space along the way. But if the necessary large tanks are not likely, it is best for the fish to re-home them now before things progress further.

The Red Tail Black Shark is not a peaceful fish. For reasons we don't understand, it frequently suddenly takes a real dislike to vertical striped fish...angelfish for example. They will be dead overnight if this occurs.

In addition to actual physical aggression, there is the chemical signals fish release and other fish read. Phermones and allomones. And these can procliam aggression of "x" fish to others and be just as stressful. And stress is the direct cause of 95% of all aquarium fish disease.