Right advice for a new fish keeper with an inherited tank

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sabinas

Aquarium Advice Apprentice
Joined
Oct 10, 2024
Messages
11
Location
Belgium
Hello,

My neighbours are moving and presented me with their 20 gallon fish tank which they have had for four years. There are four neon tetras, one shrimp, and a LOT of assassin snails inside as well as one plant. I would like to take good care of it and have been reading a lot online but I am confused about 3 questions:

The guy at the pet shop told me that neon tetras should be in a bigger group, that four is not enough, and I should buy more. This seems to be backed up by what I read, which also says they like more plants or places to hide. But on the other hand the neighbours say the fish have been happy like that for ages, so maybe better not to disturb them? I am a bit intimidated by the idea of starting a second quarantine tank which sounds necessary for adding more fish and even plants.

For the water changes, the neighbour told me I could change it once every 6 weeks or so, and test the water about a week after the change. But online it looks like changing less of the water much more often would be better, and testing more frequently? I don’t want to mess with a system that is working but I do want to look after them properly.

There is sand at the bottom of the tank with what looks like black algae on the glass. I read online that you can run your finger along the glass and remove it. I tried this with a small section and the algae went away but of course it disturbed the sand, which I also read can be fatal for the fish! Should I try to clean this slowly or just let it be? Is there a better way to clean it?

Would really appreciate any views from experienced fish keepers, thank you so much!
 
Tetras are social fish and do better in bigger groups. 4 fish is better than 3, 6 is better than 4, 10 is better than 6 etc. Do you "need" to get more neons? No. Would they do better in a bigger group? Almost certainly. They will feel more comfortable, act more naturally. There is always a risk that adding new fish is detrimental. Maybe one of the new fish is a jerk and bullies the others. Maybe you accidentally introduce an infected fish and this passes onto the 4 fish already in your aquarium. This is something you will have to make your own decision on, but you have a lot of scope to add more fish if you wish.

A water change every 6 weeks isn't very much. A fully stocked tank should have half the water changed every week. A lightly stocked tank might only need a third of the water changed every 2 weeks. 4 neon tetras isn't very much, and a water change every 6 weeks might be sufficient. If we knew the water parameters in the tank it would be a good guide as to whether a water change every 6 weeks has kept water quality at a good level. In particular nitrate. And we have to take account all these assassin snails too. Get the water tested to see where we are. pH, ammonia, nitrite and nitrate. Don't do anything too drastic to start with. Maybe a small 10% water change after the water test while we figure out what your plans are for the tank.

When you are comfortable with your water parameters then you test less. You might want to do daily tests for a few weeks after the move to make sure everything is safe, but once you are comfortable they are stable you might go years without doing a water test.

Potentially toxic gasses can build up in sand substrates, and when the sand is disturbed it releases into the water and can kill the fish. It's a good idea to periodically disturb the sand so these gas pockets dont develop, but we have no idea if the previous owner did thus. I presume this algae is on the glass and below the substrate? Cleaning this off isn't going to disturb too much substrate, only a small amount close to the glass. I use a cheap toothbrush.

Are you sure they are assassin snails? Can we get a photo? How big are they? You should be able to rehome a lot of these if you wish. Maybe get some store credit from your fish store. I'm surprised they haven't eaten your shrimp.
 
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Here is a thread I wrote about the difference between and setting up a quarantine tank and a hospital tank to help guide you. Neither is really complicated. (y) Quarantine tanks and Hospital tanks, are they really different?

What Aiken said about bringing new fish in is the sad reality of today's hobby. So many fish are now being farm bred and raised and unfortunately, not all farms use either a natural or holistic method of fish raising so you have to look at every new fish as a potential disease carrier so using a quarantine tank for any new fish is highly recommended for the safety of your main tank's population.

Hope this helps (y)
 
Thank you so much to both, REALLY appreciated. I think then I will wait a little bit and get used to taking care of these fish before adding new ones, if it’s not urgent to do it right away. I tested the water and it told me too much hardness and too much chlorine and that I should do a water change with more water conditioner, so I changed about a third of the tank like this.

I add a photo of the snails, the pet shop guy tell me it’s an assassin snail but I’m not sure! Also not sure if I should be giving extra food for them, at the moment I am giving powder food in an amount for just the fish.

Also a photo of the algae, a bit where I cleaned and a bit where I didn’t, hoping I didn’t poison all the fish like this!!!
 

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They do look like assassin snails, although the photo isn't clear. When you said a LOT I was expecting hundreds, like the photo below. You could possibly sell them (or some) if you wanted, they are an in demand species.

ccabf37785048eb993ca7769fb35fa1b.jpg

They will happily feed on leftover food, if you wanted to give them some specific food, something like Hikari Crab Cuisine pellets would be good. If you don't want them breeding and overpopulating the aquarium I'd probably not feed them and make sure you aren't overfeeding the fish.

I think its safe to clean up the algae. Give it a wipe before you do a water change so you can syphon out the algae from the water.

What precisely were the water parameters when you tested. Particularly interested in nitrate. Chlorine is never good, make sure you use enough water conditioner to treat the whole 20 gallons every time you do a water change. If your test still shows chlorine afterwards, add more water conditioner and know you have to add more than a normal dose going forward.
 
OK thank you very much, then I won’t give extra food for the snails! And really helpful to know that I can add water conditioner for the whole tank, I was trying to dose it relative to the new water I was adding so probably that’s causing the problem!

For the water parameters this is the test strip this morning:

nitrate (NO2) 0,25 mg/l
nitrate (NO3) 18 mg/l
General hardness >21 dH
Carbonate hardness 10 dH
ph value 7.2
Chlorine 0.8 mg/l
Carbon dioxide 15 mg/l

Thank you so much for this advice, it’s really really helpful.
 
A few points on test strips.

They aren't very reliable. You can't really trust the results you get from them. They might be accurate, they might not. A liquid test kit like API Freshwater Master Test Kit is going to be more reliable.

Those 5 in 1, 6 in 1 etc test strips don't test for ammonia. You have to buy the ammonia test strip separately. Ammonia is the most important test as that's the first parameter that is going to go off.

Test strips are expensive per test. A pack of API test strips costs about £10 and you get 25 tests, so that's 40p per test. And you also have to buy the ammonia test strips on top of that. You can pick up the liquid test kit I mention for about £30, but you get hundreds of tests for your money. So while it's more money up front, liquid test kits are more cost effective and include all the tests you need. A tip for getting the most bang for your buck with test strips though. Cut them in half length wise with some scissors, get 2 for the price of 1.

Lets say the tests you have done are accurate though.

NO2 is nitrite, not nitrate. That should be zero. This shows your aquarium isn't cycled. Maybe things got disturbed in the move, maybe you tried to clean something like the filter and effected your cycle. More on this later as i suspect i know whats happened. While the nitrite should be zero, 0.25ppm is safe. But you don't want it any higher. If your test shows nitrite any higher than that do a water change.

Nitrate. That's a good level and a good sign that you dont need to be doing water changes too often (although id still do them more frequently than every 6 weeks). Below 40ppm is usually considered acceptable. Below 20ppm is good. Below 10ppm very good. This is a sign that your cycle is functioning, but with the nitrite, not functioning as well as it should.

You have very hard water. That would suit some fish, but not others. Tetras are soft water fish, but they seem to be living in it OK, so I wouldn't worry about it. Trying to adjust water parameters would do more harm than good. But something to consider longer term if you decide to get more fish.

Chlorine should be zero. This shows you haven't used enough water conditioner. Add another dose as a matter of urgency. Chlorine kills bacteria, and bacteria are what cycles the aquarium. This might be what's affected your cycle. Check with your water company whether they treat your water with chlorine or chloramine. Do a chlorine test on your tap water.

What water conditioner are you using?

Do you understand what I mean by your "cycle"?

You need to have a test for ammonia. Your cycle isn't functioning properly and that will likely result in ammonia. Without a test we don't know how much ammonia is present.
 
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OK I will get this liquid test kit! For the moment I am using all the stuff the neighbour left me with the tank and it is little strips so I still have a lot of these. I have added another dose of the Biotopol to the tank and will test it again tomorrow morning then to see if the chlorine changes.

Is there a maximum amount of water changes I should be doing? I mean, should I change a bit every day until the water gets better? Or would that be too much and bother the fish also? I’m afraid I don’t really understand how the cycle works yet but what I grasped was that it means whether your tank has enough bacteria in it to eat all the fish waste.

I guess the fish must be used to the hardness of the water since they’ve been living in the building for so long. But good to know at least this I don’t have to worry about immediately.

Thank you so much for the super detailed replies, I’m feeling very daunted by this tank now taking over my living room and it’s such a relief to have some expert advice !
 
So, for your 20 gallon/ 80 litre aquarium you should be adding 40ml of the biotopol with every water change. Your water conditioner should work instantly on contact, so you test the water for chlorine after 15 minutes once the water has had chance to thoroughly mix.

Next money saving tip. When you have used up all your biotopol, dont buy any more and get either Seachem Prime or API AquaEssential.

500ml of Biotopol costs about £16 and treats about 2000 litres of water. So every water change on your 80 litre aquarium will cost you about £0.64p. 500ml of Prime costs about £21 and treats 20000 litres of water. So every water change on your 80 litre aquarium would cost £0.11p. So a water change costs 6x more using Biotopol as opposed to Prime. AquaEssential is a similar cost/ water change as Prime. And both Prime and AquaEssential have a few bells and whistles that make them far better water conditioners. Use up the water conditioner you have been given, but when it comes to buying new there are better, more cost effective options.

While you arent cycled you need to do sufficient water changes to keep your water safe. The only parameter we know is off is nitrite, and it's not so high that a water change is required. But we don't know where your ammonia is. A daily water change until you can test for ammonia might not be a bad thing. But, we don't know if your water is chlorine or chloramine treated. Chloramine has some ammonia in it, so doing a water change because there is a little ammonia in your aquarium water might be pointless as the new water might contain ammonia as well. Doing a small 25% water change every day until you can test for ammonia should be ok though.

You have summed up the nitrogen cycle pretty accurately.

Yes, your fish will have acclimated to the water they live in. If you suddenly tried to change the hardness to something they would normally prefer, the change could kill them.
 
It looks like none of my test results are accurate at all because I did several tests and the results came out wildly different each time. So either I’ve been totally messing around with the water, or these strips are completely useless.

I couldn’t find any of the liquid test kit you recommended at the shop so I will have to order it online, but I could find one testing NH4 which was the closest thing I could find to an ammonia test. If I can trust this test, it came out on the lowest level, <0,5 mg.

I guess I will keep changing the water every day until I can get a more reliable test and hope for the best!
 
Could you post a photo of the NH4 test kit?

NH4+ is ammonium, most ammonia test kits are for ammonia (NH3) and ammonium (NH4+). That's what you want.

I've never seen a test for just ammonium before.

If it's an ammonia test then it indicates you need to change water. 0.5mg/l is a little too high.

As said, test strips are unreliable, especially if they've expired.
 
This is the test, it doesn't show anything less than <0,05 mg. But the colour looks to me like it matches this. If I put it on the second hole (0,1) the control colour is definitely darker than my tested water.

Huge thank you for all your help!
 

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That's fine as an ammonia test. The first reagent will acidify the water and the free ammonia (NH3) will turn into ammonium (NH4+), and the other 2 reagents will test for the ammonium. So the packaging is correct that the test is only for ammonium, but as all the free ammona has turned to ammonium, the outcome is a test for free ammonia + ammonium. This is the same as most home test kits for ammonia.

If JBL liquid tests are what you can more easily get hold of in your location, they will be fine rather than the API one I suggested. The API one is the most commonly used one, they are usually readily available everywhere, and most hobbyists will know how to use them, but other test kits are available. Just get hold of tests for pH, nitrite and nitrate. JBL do a "combitest" kit that covers these plus a few other tests. They also do a "lab" test kit that covers everything you might possibly want to test. They do look a bit pricey here in the UK.
 
Tetras are social fish and do better in bigger groups. 4 fish is better than 3, 6 is better than 4, 10 is better than 6 etc. Do you "need" to get more neons? No. Would they do better in a bigger group? Almost certainly. They will feel more comfortable, act more naturally. There is always a risk that adding new fish is detrimental. Maybe one of the new fish is a jerk and bullies the others. Maybe you accidentally introduce an infected fish and this passes onto the 4 fish already in your aquarium. This is something you will have to make your own decision on, but you have a lot of scope to add more fish if you wish.

A water change every 6 weeks isn't very much. A fully stocked tank should have half the water changed every week. A lightly stocked tank might only need a third of the water changed every 2 weeks. 4 neon tetras isn't very much, and a water change every 6 weeks might be sufficient. If we knew the water parameters in the tank it would be a good guide as to whether a water change every 6 weeks has kept water quality at a good level. In particular nitrate. And we have to take account all these assassin snails too. Get the water tested to see where we are. pH, ammonia, nitrite and nitrate. Don't do anything too drastic to start with. Maybe a small 10% water change after the water test while we figure out what your plans are for the tank.

When you are comfortable with your water parameters then you test less. You might want to do daily tests for a few weeks after the move to make sure everything is safe, but once you are comfortable they are stable you might go years without doing a water test.

Potentially toxic gasses can build up in sand substrates, and when the sand is disturbed it releases into the water and can kill the fish. It's a good idea to periodically disturb the sand so these gas pockets dont develop, but we have no idea if the previous owner did thus. I presume this algae is on the glass and below the substrate? Cleaning this off isn't going to disturb too much substrate, only a small amount close to the glass. I use a cheap toothbrush.

Are you sure they are assassin snails? Can we get a photo? How big are they? You should be able to rehome a lot of these if you wish. Maybe get some store credit from your fish store. I'm surprised they haven't eaten your shrimp.
Your bio load is not that high I wouldn’t d any water changes until nitrite levels get above 40ppm
 
Your bio load is not that high I wouldn’t d any water changes until nitrite levels get above 40ppm
Water changes are for other reasons than just controlling nitrate. They replenish essential minerals, and removes harmful organisms for instance.

Only doing water changes when nitrate get high is a really bad idea. While 40ppm nitrate is considered a safe level, keeping nitrate lower is always a good idea. Nitrate is still toxic, and prolonged exposure even at 40ppm is going to cause some health issues.
 
Clown loaches will rid you of snails and they won’t bother your neons
Clown loaches can grow to be 12" long if kept in a suitable environment. Juvenile clown loaches should be kept in a minimum of 55 gallons, but eventually you would need an aquarium of 150 gallons to keep a suitably sized group of adult clown loaches. OPs aquarium is only 20 gallons and isn't suitable for even juvenile clown loaches.

Clown loaches prefer much warmer water than what most tropical aquariums are kept at. 28 to 30c/ 82 to 86f. They are also omnivorous fish and will eat anything that fits in their mouth. This includes neon tetras if they can catch them.

All in all clown loaches are a really poor choice of fish to share a 20 gallon aquarium with neon tetras.
 
I got the liquid test kit and it all looks pretty OK to me except for the PH but this you already advised me should be OK since the fish are used to it. So I'm thinking that I don't need to keep testing & changing the water every day but could do a once a week routine instead hopefully.

I have only had the fish for ten days so I'd like to just get the hang of them for a while before adding anything else and then I guess I will try to add a few more of the same neon tetras since they are such a small group at the moment. I have a smaller tank that the kids use to keep snails in, maybe this could be a quarantine tank.

I counted yesterday and I could see about 60 snails as well as the four fish. They all start climbing up the glass when I turn the lights on. Is this too many and should I try to take some out??

Many thanks for all the advice!!
 

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Yes, those water parameters look good. But you have been doing regular water changes, so they may be good because of the water changes (which is why you was doing them), or they could be good because your cycle has established sufficiently.

No need for an immediate water change, but I would continue to test daily for at least a week, and change water if you see any ammonia or nitrite in there. If after a week you are still seeing no ammonia or nitrite you can cut back on the testing and establish a regular water change routine. Maybe changing 1/3 of the water every 2 weeks might be sufficient, but I'm mindful of all those snails that will be contributing to things. You definitely don't need 60 assassin snails. I'd look to see if there is a local aquarium club you could contact and see if they have members who would take some, or a local FB group. There is some value in them as more than just loach food if you wanted to sell them and there are enough local hobbyists.
 
The aquarium hobby is great and there are alot of different opinions, I prefer heavily planted tanks, alot of filtration, and variety 😀 . Any of the fish that school I give them lots ofnfriends there personalities will be so much better. I have found this to be a great tube for information Aquarium Co-Op
 
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