Community fish becoming agressive

Hi, I'm a begginer in this hobby. I have a 72G fresh water tank, that I have been trying to set up with some community fish. I was going by a little compatibility chart they gave me at petco, and by the fish at petsmart that said community fish (since they informed me they would be fine with each other.
I have 3 goldfish (which seem to have been losing some of their scales), 5 buenos aires tetras, 5 skirt tetras, 5 red glass barb, 2 algae eaters, 3 (black mollies, found one dead and can't find the other one), 5 dalmatian mollies, 4 silver mollies, 2 guppies (found 2 of them almost all eaten and 1 dissapeared),
The buenos aires tetras and the goldfish are the biggest ones in the tank. The Buenos aires tetras seem pretty aggressive specially the biggest one of them (about 3"). I have been doing water changes about every week. The aquarium have been set up for about 2 months.
I brought the water to be tested at petsmart and they said all the levels were fine,
Could I be not feeding them enough and its causing them to be more aggressive?

 

Welcome to FishLore!

Little bit of advice for newbies to the hobby: don't always follow what fish or pet stores tell you. A lot of times they are wrongly informed, and will wrongly inform you too. Always research for yourself first!

Many of the fish you listed are in fact not very compatible with each other.
- Goldfish are cold-water fish, can get very large, and are very messy,
- Buenos Aires tetras can be major bullies, and I'm guessing they are the reason why some of your fish are disappearing.
- Depending on your algae eaters, they might get very large and possibly aggressive...

The barbs, skirt tetras, mollies and guppies should be fine as long as they are not picking on each other, but what type of algae eaters do you have? If they are Chinese algae eaters you might want to consider getting rid of them, they can get VERY large and will get very aggressive as they grow. If they are common plecos, you still should probably consider getting rid of them as they too get very large and have a great bioload. They may be fine in your tank for a while, but eventually they might start to cause problems.

Also, your profile states you do not know the Nitrogen Cycle. <--- Click the link and read it, it's a VERY important part of keeping fish! You might want to test your water for yourself by the way. I'm not sure if Petsmart uses strips or not to test water samples, but if they do those aren't usually very accurate. I'd recommend getting the API Master Test Kit as it is very accurate and pretty easy to use

 

Thanks a lot, the algae eaters are just regular plecos, and right now they just seem to be hiding most of the time. And from what I understood of the nitrogen cycle is something that needs more attention when establishing the tank, am I wrong on that understanding? Cause I did the steps to try to be ready to go, put some bacteria and let it sit for a few days and then had 3 goldfish in there for about a month.
Also, when you decide to get a fish out of your tank, what do you do with them?

 

Plecos aren't algae eaters, sorry to tell you And depending on species, they can get to 2 feet long! Big, messy fish

What you have in your tank is a mix of tropical and temperate fish. They will *probably* be fine together, but the goldies really should not be in a tank with tropical fish, as water temperature requirements are vastly different between the two.

In order to reduce aggression with your schooling fish, get more of them. Schooling fish tend to do one of two things when the schools are too small for their liking: they hide nonstop, or the go on a rampage and attack all the other fish. If you keep larger schools, you should see less aggression and have a happier tank.

Do be sure not to overstock the tank, though, especially with messy fish like goldies and plecos. (personally I would rehome both of these).

 

Thanks a lot, the algae eaters are just regular plecos, and right now they just seem to be hiding most of the time. And from what I understood of the nitrogen cycle is something that needs more attention when establishing the tank, am I wrong on that understanding? Cause I did the steps to try to be ready to go, put some bacteria and let it sit for a few days and then had 3 goldfish in there for about a month.
Also, when you decide to get a fish out of your tank, what do you do with them?

Then you did correctly, adding live bacteria it is more important at the start of a tank, yes, but you still of course need to monitor it so that nothing toxic gets out of hand and harms your fish.

Did you mean getting rid of a fish? You might be able to take them back to where you got them.

Also, junebug mentioned something I forgot -- you probably should add a few more fish to your schools, that should help

 

the nitrogen cycle is something that needs more attention when establishing the tank, am I wrong on that understanding?

Yes and no. You're right in that it's important to pay attention while getting the cycle going when you first begin a tank. But it still requires attention even after the cycle is complete. Getting the cycle going and keeping the cycle going are as equally important. I'll take a wild guess here that you have the API Liquid Test Kit for freshwater tanks. If you look in the back of the instruction booklet you will notice that there is a log. Beginner aquarists should keep a weekly log of their water parameters. You perform all tests each week on the same day that you do your tank maintenance just before the water change, and you log the test results. After awhile you will get to know your tank and will not need to log, and once you really really get to know your tank you may not even need to perform those tests. You'll just know from experience (by fish behavior) if something is off.... then you'll want to do a test.

Keeping a log as a beginner will help in several ways; you'll be able to tell when something is wonky, you'll have the information readily available should you need to seek the advice of a veterinarian, or if you ask for help here on the forums. You'll find that it's the first thing we ask for are parameter readings. A lot of things can affect the nitrogen cycle long after the cycle is started, so keeping a close eye on things is important for a beginner.

 

Should I get more even of the fish that are the aggressors (the buenos aires tetras) ? Or just of the ones that are being attacked?

 

and also, I have black mollies, dalmatian mollies and silver mollies, a total of 12 mollies. Do those count as one school or should I get more of each one of them?

 

We need to know if those are common pleco or not.

 

Here is the link to the ones I have!

 

and also, I have black mollies, dalmatian mollies and silver mollies, a total of 12 mollies. Do those count as one school or should I get more of each one of them?

They'll be fine, there's plenty of them and they're all the same so they'll be happy

I would get more Buenos Aires, yes, that probably would help limit the aggression since they'll have more buddies to make them feel more comfortable and to disperse any aggression that does come up, but, I would still add more of the barbs and skirts, they can get a bit nippy too if their numbers are too few.

And yes, those are common plecos that you have, and they tend to be very messy like goldfish (plus the added fact that they can grow over 2 feet). I would find a new home for them soon, though at the size they probably are now they should be fine for a little bit.

By the way, what kind of goldfish do you have? Are they fancies or comets?

 

I'm not sure about the goldfish, they are the really cheap ones. I believe I paid 20c for each!

 

Most likely commons they can get huge as well

 

I'm not sure about the goldfish, they are the really cheap ones. I believe I paid 20c for each!

Yup, those are most likely feeder comets. They will get very big also, a foot long or maybe more. They probably would be fine for now, but eventually you will want to get rid of them, or maybe, if you can, get a pond for them.

 

I'm not sure about the goldfish, they are the really cheap ones. I believe I paid 20c for each!

Those where feeder did you quarantine them. To make sure they didn't have any disease or parasite.

 

Those where feeder did you quarantine them. To make sure they didn't have any disease or parasite.

I'm pretty sure he said he's had them in there for quite a while and before any of the other fish, so I think they're okay

 

No I did not.