Input? Angelfish suddenly very aggressive after tank cleaning and decor change

[NoLa24]

I'm hoping someone can shed some light on my problem:
I have a 39 gallon tank with a school of 7 cory catfish and 2 large male angelfish. Everyone has been living together for well over a year, quite peacefully. The angels were introduced to each other already full grown and never fought even upon meeting.
I typically do 1/4 water changes once a month and every yr or so I do a full cleaning.
It was about that time and I had been wanting to change out the substrate from gravel to river rock so decided it would be a good time. I relocated everyone (as well as the live plants) to a 10 gallon tank with an air stone for about 24 hrs with zero issue.
Once I had all the new rocks set up and what not I let the pump cycle the water for over 12 hrs before putting everyone back (i did add back the 10 gallons of water to the new water).
I put them back right before bed and in the morning i went to check out the new setup and much to my shock one of the angels was repeatedly attacking the other one. To the point that he had a bloody bruise spot on his back.
I removed the injured one right away and tested the ph, which was perfect, and tested for ammonia wich there was the smallest trace detected, although not surprising given the level of stress that was going on.
As i was testing i noticed that all of the corys were not as lively as usual and were quietly hanging out at the bottom on whichever side the angel was not on.
The injured one is currently in a 10 gallon and doing well and the corys have returned to there normal spunky selves but I'm not sure want to do about re-introducing my angels? I could maybe see if the one just took great exception to a habitat change but i checked on them frequently while they were all crammed in the 10 gal and he was being docile as always (as was everyone). Has anyone experianced this before? Any advice?

 

[Colin_T]

I typically do 1/4 water changes once a month and every yr or so I do a full cleaning.

You would be better off doing a 50-75% water change each week and using a gravel cleaner each time you do a water change. Using a gravel cleaner and doing regular water changes will mean you never have to strip the tank down and do a major clean. The link below has a base model gravel cleaner that every aquarium keeper should own.
https://www.about-goldfish.com/aquarium-cleaning.html

Fish live in a soup of bacteria, viruses, protozoans & fungus and doing big water changes dilute these microscopic organisms and keep their levels low so they are less likely to impact on the fish's health. In addition to these micro-organisms, fish release chemicals into the water and the pH can drop due to acids from fish food and waste, and nitrates can build up. And their water is also filtered through their own waste. Basically fish live in a sewer of their own crap.

If you only do a monthly water change then these chemicals and disease organisms build up and stress the fish. When you do your monthly water change and the new water can be completely different to the aquarium water because the tank water quality has deteriorated due to the abovementioned substances. This stresses the fish out more.

By only changing 25% of the water you are only going to dilute the disease organisms, chemicals and waste by 25%. Bigger water changes dilute these much more effectively. So a 50-75% water change each week is a much better for the fish than a 25% water change each month.

Gravel cleaning (using a gravel cleaner) is also something that should be done to remove the gunk that collects in the substrate.

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Filters should be cleaned at least once a month or every 2 weeks if possible. The filters traps the fish waste and all the aquarium water gets filtered through the waste. Keeping the filters clean means the fish live in cleaner water and are not living in their own crap.

Filter materials should be washed out in a bucket of tank water.

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I removed the injured one right away and tested the ph, which was perfect, and tested for ammonia wich there was the smallest trace detected, although not surprising given the level of stress that was going on.

I am not sure if you kept the filter running on the 10 gallon tank while you changed the big tank. However, if you turned it off, the ammonia could be from the filter bacteria dying due to lack of oxygen if the filter was turned off for more than a couple of hours.

The ammonia is unlikely to be from stress and is more likely from changing the substrate or filter die off.

Monitor the ammonia and nitrite levels over the next few weeks and do a 75% water change if you get any readings above 0.0

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Onto your issue of aggression. You changed the environment and broke up the established territories and now the males have decided to make the tank their home. You will probably have to keep them separate from now on.

If you had left the fish in the tank and removed the objects, changed the substrate and cleaned the tank with the fish still in it, this might not have happened.

 

[NoLa24]

I do use a vacum cleaner, isn't that part of what a partial water change is? I change the filter cartridge monthly and check ph and such as well and my tank is always sparkling clean and numbers are on point.
What i mean when I say an annual cleaning is that i take all non living decor out and give it a good washing and at that point i do a 3/4 water change. I merely removed the gravel to replace with river rock. If the tank is clear and clean and all fish are healthy then why mess with it?
They have been seperated for only a day and the large tank is at 0 ammonia (no water change done) the small tank has trace amounts despite 2; 1/4 water changes 12 hrs apart.
But thank you for the lecture on tank cleanliness.

 

[NickAu]

Onto your issue of aggression. You changed the environment and broke up the established territories and now the males have decided to make the tank their home. You will probably have to keep them separate from now on.

If you had left the fish in the tank and removed the objects, changed the substrate and cleaned the tank with the fish still in it, this might not have happened.

Spot on.

 

[Colin_T]

You should not be changing filter cartridges because you lose beneficial filter bacteria when you do. If you have carbon in a filter pad, you can cut the pad open and throw the carbon away and keep using the pad. Just give it a squeeze in a bucket of tank water every 2-4 weeks.

If you don't have sponges in the filter, most external power filters can have sponges added to them. There are numerous brands of sponge and you can even get round ones with a hole through the centre and these can go on the intake strainer of most filters. If you have several sponges and the cartridge, then you could replace the cartridge and the sponges would still contain plenty of filter bacteria to keep the ammonia at 0.

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If the tank is clear and clean and all fish are healthy then why mess with it?

I refer back to my original post about fish living in a soup of microscopic organisms and their own waste.

Fish may appear healthy but if they are in water full of disease organisms, their own waste and high nitrates, they will be stressed and their lives can be shorted due to the stress.

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re: cleaning décor annually. Most people simply take ornaments out whenever they need a clean, rinse or hose them off and put them back in the tank. Do a bit here and bit there and it means you don't have to do a big spring clean once a year.

 

[NoLa24]

Ok but if I test the water parameters routinely and they are WNL, the water is clear, and my fish always live longer then the average lifespan, then common logic would say "if it ain't broke don't fix it". They are not living in a disease ridden pool. You keep going on about the ammonia, but as I said the larger tank is at zero since I seperated them and the small one tested zero this morning. Again common logic would reason that this is from stress reduction (as it is common knowledge that stress in a fish tank will up the bio load).

 

[Byron]

I am going to try and explain further what Colin has been posting, as it is correct but may not be fully understood. I know that a clear-water aquarium gives all of us the impression that it is clean, but this is often far from true. Clear water and clean water are two very different things.

Before I get to that though...two male angelfish are not at all likely to get along long-term. Angelfish are shoaling (this is programmed into their DNA, so we are not going to change it) and live in smallish groups; in an aquarium they should never be less than five, unless it is a bonded and mated pair used for breeding. Males are very territorial, and individual fish can express this to varying degrees. And while two males may seem to be getting along, we cannot possibly tell just what they are experiencing/thinking. Some environmental issue frequently sets this off, as here. Separate them, or the subordinate will be dead before too long. But having said that, are you certain they are both male? Both could be female, which can mean more harmony though not always, or they could bee male/female not bonded and these can sometimes suddenly decide enough is enough.

Back to the water changes. First, please always give us test numbers, since we cannot ascertain what you might mean by within normal limits (I assume this is what WNL means) or the pH being "perfect." Zero is the normal limit for ammonia and nitrite, nitrate should be as low as absolutely possible continuously, and never be higher before a water change and then lower after, building up to the next water change. That means insufficient water is being changed, or organics are accumulating beyond what the system can handle, which can sometimes be associated with too many fish, too large sized fish for the system, or overfeeding. And inadequate substrate cleaning, filter cleaning, all contribute. Nitrate should as I say be as low as possible, never above 20 ppm, and it should remain stable from water change to water change. My tanks all run in the zero to 5 ppm range, and have for years. I do 60-70% water changes once a week. Filters are rinsed at every water change. Substrate is not usually touched as that is the primary bed for many types of bacteria, aerobic and anaerobic, nitrifying and de-nitrifying. And I have live plants in all tanks which makes a difference. Similarly the ph should be exactly the same, within a decimal point or two, every time tested; test at the same time of day as pH does fluctuate a bit during a 24 hour period, and testing at the same relative time will give you certainty as to what it is doing. Always test prior to any water change; also testing after is fine, but should not be used as the "probable norm" for the tank.

While nitrate and pH can be easily tested and some may use this as a guide to water changes, by the time these tests show a need for a W/C it is frankly too late. The fish are already being affected. And there are substances in the water we cannot test for in any viable way as aquarists. TDS (total dissolved solids) build up (a TDS meter will test this) and the higher the more they affect fish. Fish release pheromones and allomones, chemical signals other fish read, and these build up until we remove them with a water change. In the natural habitat, water volume compared to fish mass is very much different from even the most understocked aquarium; fish do not live in the same water from one respiration to the next. We cannot possibly reproduce this in an aquarium without complete flow-through water, which none of us has. Fish will always be healthier with substantial water changes. A healthier physiology means less stress on the fish's metabolism, and better disease prevention.

The reaction of the cories alone shows there was a significant issue. More substantial water changes regularly should prevent this.

Hope this helps explain what Colin was getting at. We are here to help.

 

[NoLa24]

As I stated earlier, I test the numbers at least once a month not just after a water change. I only tested AFTER this time because of the issue. I understood what he was saying I just didn't agree with it.
I have had the two males for nearly a yr and a half and this was the first issue they've had. Both were introduced as adults with no females. In regards to "programmed DNA" many experienced angel breeders will tell you that through captive breeding a lot of the aggressive traits have been bred out and many are quite docile now. One of my males was part of a breeding pair but took to the new male very well (again over a yr ago).
But anyway on to the update:
After allowing the injured one to heal in the small tank which he completely did, i switched the two of them and put the attacker in the small tank for 2-3 days. Yesterday i placed him back in the large tank and no issues between them since. They have been swimming around together like nothing ever happened.