First freshwater aquarium - please help a newbie out?

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elcapitanl

Aquarium Advice Newbie
Joined
May 12, 2025
Messages
3
Location
Los Angeles
Hi everyone -

I just started a new 21.6 gallon freshwater aquarium (see picture attached). I got 5 feeder guppies to start the cycle - 4 females and 1 male. I got a few live plants (hornwort and water wisteria) all throughout but I’m wondering if that’s too much here?

Also, I’ve noticed that my male guppy (also the smallest of the bunch) tends to hide inside the castle and absolutely does not come out. My main concern is that he’s not eating. However, I also noticed during the first two days I had him he stays towards the bottom and catches the food that ends up crumbling down. Should I be worried if I don’t see him come out at all? Today (Sunday/Mother's Day), when I fed the guppies, I noticed only 4 of the females were actively feeding so I got worried the male was dead. I had to move the castle in picture twice to make sure he was still alive today - but after realizing he is, I just stopped because I did not want to keep stressing the fish.

Note that I added the fish 2 days ago so this aquarium is fresh as of last Friday. All fish are currently doing well after 48+ hours of being in the tank. I would appreciate any and all suggestions. Thank you in advance!
 

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5 fish in an uncycled tank to start your cycle is quite a lot. You normally want 1 small fish/ 10 gallons when you start a fish in cycle, so that would be a couple of fish. It's possible that so heavily stocked that water parameters are getting elevated in a couple of days. So let's start there, what are your water parameters? And what test kit do you have?

How did you acclimate your fish into the aquarium?

Going into the hobby it's a good thing to understand that not every fish you buy will be healthy and part of the quarantine process is removing the unhealthy fish before they go in your main display tank.

This is also a good opportunity to consider what plan you have for these fish breeding. Guppies, like livebearers generally, are prolific breeders. There is a good chance your females are already pregnant as they've been kept with a male. If they are, the fry will start breeding in a matter of months, then they will produce more fry, which in turn will produce more fry, etc etc etc. Your 20 gallon aquarium will quickly get overrun, and then you need a plan as to what do with all the fish. If you don't intend breeding guppies with a good plan in place for what to do with hundreds of fish, only keep male guppies.
 
5 fish in an uncycled tank to start your cycle is quite a lot. You normally want 1 small fish/ 10 gallons when you start a fish in cycle, so that would be a couple of fish. It's possible that so heavily stocked that water parameters are getting elevated in a couple of days. So let's start there, what are your water parameters? And what test kit do you have?

How did you acclimate your fish into the aquarium?

Going into the hobby it's a good thing to understand that not every fish you buy will be healthy and part of the quarantine process is removing the unhealthy fish before they go in your main display tank.

This is also a good opportunity to consider what plan you have for these fish breeding. Guppies, like livebearers generally, are prolific breeders. There is a good chance your females are already pregnant as they've been kept with a male. If they are, the fry will start breeding in a matter of months, then they will produce more fry, which in turn will produce more fry, etc etc etc. Your 20 gallon aquarium will quickly get overrun, and then you need a plan as to what do with all the fish. If you don't intend breeding guppies with a good plan in place for what to do with hundreds of fish, only keep male guppies.
Thank you very much for your detailed answer. Unfortunately, I woke up this morning to see that the 1 male was floating dead. Do you recommend I test the water today? I just got the API Freshwater Master test kit.
I acclimated the fish by letting them float in the water for 20-30 minutes in the bag. Then, I opened the bag, and dropped a few tea spoons of the tank water into that bag while they were acclimating still. I gave that another 15-20 minutes of repeating that process until I dropped them all in.
 
Always useful to know what your water parameters are.
I ran the ammonia test, and it seems to be either yellow (around 0 PPM) or slightly close to 0.25 PPM (hard to tell with this color - I attached a screenshot). Nitrite is absolutely 0. Nitrate is at 0. pH is at around 7.6.

Any ideas on why the male guppy could have died and any further steps I should be taking? As I mentioned, rest of the fish look fine.
 

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Like I said not every fish will be healthy. It's not uncommon for unhealthy fish to die from the stress of the move.

There is a bit of ammonia in there, test daily, if the ammonia gets any higher than that change some water. Don't add any more fish until you are consistently seeing zero ammonia and nitrite over a week, and then only add another fish or 2 at a time and continue monitor.
 
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