White Cloud Mountain Minnow (WCMM) behavior in new tank


HI everybody!

I am new to the fishkeeping hobby (I had a betta before but that was a while ago and I was not as well-informed about keeping an aquarium back then). Thanks for reading and I'm hoping someone can help me with figuring out what, if anything could be wrong in my tank.

About my tank: 10G kit by Aqueon, came with filter, LED lighting and heater included. Heater is set to 78F (preset) but it keeps the tank around 77 according to my floating thermometer. I also have indicators for the pH and Ammonia. To setup I bought plenty of gravel from my local co-op who have fantastic ratings and locally bred fish, and they care a lot about fish. I purchased 5 WCMM (I believe there are 2 males and 2 females for sure - the 5th might be a male or a rather young female, I am not sure.)

I know cycling should ideally not be done with fish but the co-op is quite a drive, so I asked them the best way and best fish to experience the least stress. I started with Stability by seachem, 6 plants all over the tank, plant fertilizer, water conditioner, and a piece of driftwood and a bag of shells to increase the hardness of the water as it's really soft where I live. I set it up with the plants, gravel, driftwood, shells (I boiled the shells and driftwood and filtered it out). I have been following the stability directions carefully and also the water conditioner, and did one 25% water change on day 3 to make sure there was no ammonia buildup. I also purchased pH down and strips to check water quality.

Today is day 6 and the plants seem to be doing fantastic, the tank appears great. pH is slightly high at 7.4 over the last 5 days (constant) and temp was always at 77. Ammonia always at 0. I tested water today and everything looks okay except pH was little high as mentioned above. Nitrate is under 10, nitrite & ammonia are 0, water is just about average on hardness scale and chlorine also 0. I fed them only starting day 2 morning and am powdering the little balls into tiny particles.

The problem (maybe): As of day 1 the WCMM were tightly knit (seemingly classic schooling behavior) but as of day 2-3 they were much more active and all over the tank, between the plants, behind the filter and didn't bother sticking together. The males also appeared to be chasing each other every now and then and flaring at each other quite a bit. As of today day 6 one of the little males appears to be the aggressor in the tank - he is chasing everyone around with apparently intent to bite (or just chasing, not sure) and when he gets close to the other males or females he flares up and they all run away. He also chases the others away sometimes when I feed them in the morning - I am feeding them not too much, they get through it in about a minute. The females appear very happy and so does the other fish who I am not sure is male or female, but this guy is always chasing the others and appears a little less colorful. I'm not sure if he's stressed for some reason or this is just one aggressive guy? I was thinking of getting a coupel other fish (maybe 2 otocinclus to add some more color to the tank).

Am I just overreacting or doing something wrong with the tank? Thanks so much


First off is your local coop aquarium co-op in Washington, if so he has a great YouTube channel which I highly recommend

As for your question it sounds like normal WCMM behavior (unless the aggression is to extreme ex: visible injuries on the other fish)

I wouldn't get otocinculus in a 10 gallon although a lot of people recommend it I find that they do much better in tanks of at least 30 gallons and in groups of at least 6, instead you might try some pygmy corydoras which are great community fish and a group of 6 would fit in with the WCMM (as long as you do remember to do 50% WC twice a week)


Thank you very much, I'm not as concerned now. Yes, it is Aquarium Co-op in Washington! I wil make sure to check the youtube channel. Thanks for the suggestion of dwarf cories as well. Would there be other fish you recommend (if not for cory cats) that will not overcrowd the tank?

Thank you.


I would not do any cories, even pygmy, in a 10g. They are most comfortable in schools of 6+, and spend almost all their time at the bottom. A 10 gallon doesn't have a big enough footprint.

Someone correct me if I'm wrong, but I believe WCMMs are cold water fish, which limits your options. You could do shrimp or snails.


Welcome to the forum

I agree corys and otos are shoaling fish and would do best in groups of at least 6 of their own species. They would also need a larger footprint than a 10g. WCMM's wouldn't be appropriate in this tank size either. 20 gallon minimum for them. It's possible they are being aggressive because they are not in a big enough school and not in a large enough tank.

Sounds like you could be cycled but I would also test your tap for nitrates. Also, I would stop using the pH down. Most fish can adapt to a wide pH range. You're going to encounter more problems if you try to adjust it. 77/78 is too high for WCMM's as they prefer temps in the 60's to low 70's. You could just remove the heater.


Thanks for your reply. I will not do cories, then, if it might overload the tank. The WCMM are cold water but the shop I bought them from kept the temp higher than 72, they said the WCMM would do fine at 78 (The heater is keeping it at 76-77) and they seem to have adapted well so far. Which shrimp/snail would you recommend if not for other fish?

Thanks for your reply. I read conflicting information about the tank size for WCMM - some shops/sites suggest they would do okay in a 10-gallon and others say 20, unfortunately my apartment doesn't have the space for something larger right now Do you think I could add one one to the tank to see if that helps the aggressiveness? Or would it only make things worse?

I stopped using the pH down after that first use as the pH is constant at 7.4 and the fish seem okay with it. I will test my tap water for nitrates today when doing a water change. As for the heater I'm planning to purchase a new one that I can set at 72.


I was watching a few youtube videos and particularly this one:
. My fish seem to be behaving similarly - they chase at each other and what seems like trying to nip the other but I haven't seen any injuries or marks. They also seem more aggressive when I turn on the LED lighting. Could that be a possible cause?


A lot of the advice from stores and certain sites are not reliable. I'd go with fishbase or seriouslyfish. You can see they would do much better at lower temps.


HI there, and welcome

The behaviour that you describe is pretty normal, though if it gets more aggressive than you are happy with, adding a couple more females can help. My experience so far with my schools is that more female than males makes a happy school. I had zebra danios to start with, but there were four males and two females. After one died, we had all sorts of aggression until I gave them away.....I couldn't find them in stores to expand the female population

Another thing that helps is shelter....rock caves, dense plants, etc where the harried can take off when the male gets testy

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