Hello; I see that you are being accused of overstocking. 15 to 20 (a hand full is around 5) small fish in 27 gallons does not seem overly excessive. If most of the fish were added in a short time, then the ammonia spike as already described could be the problem. On the stocking point, I have asked the folks that are quick to call a tank overstocked to justify their claims in some manner several times. So far they have not responded. (see the thread I started titled Stocking Density Opinion in freshwater general discussion section in this forum) If their claims are correct, it seems that they should be able to back them up in some manner. I have successfully kept similar numbers and more in a tank of you size.
I responded on your other thread. I have been in the hobby for a very long time. I am an advocate for high stocking levels (ask drew and mikes dad lol he will tell you we have gone head to head on stocking on various threads)
However this is not to be confused with being an advocate on NOOBS going crazy on stocking.
The reasons I suggested this are as follows
-handfull of guppies (5?) Fry (10-20) how many more will this generate in 3 months?
-guppies are messy, they are messy eaters they don't clean up after themselves
-she has the tell tail signs that her tank is in trouble
If this was someone like laura I would have given different suggestions because she has been in the hobby for a very long time, her problems are not basic. She isn't overfeeding her fish, her tank isn't potentially improperly stocked etc.
Additionally before you tear me a new one, you had a tank that had crazy high stock like 300% or so what it should have yes? how many of those fish do you still have? I have plecos that are 10 years old, I have African cichlids that are 5+ years old. So.... I think I have a decent idea what I'm talking about.
Yes heavy stocking will work for someone with decades of exp, in a large tank, absolutely this works. For someone who has a month in the hobby not so much.
You have never challenged me on a stocking suggestion, you did post a tirade that i just responded to.
Look at my stocking numbers and tell me if I am overstocked (yes way 200+ overstocked actually) my tanks stay normal because I know what I am doing.
When the OP gets the hang of it and is posting advanced questions that don't have basic root causes like high ammonia my advice will be different.
If you would like to continue this please PM me.
This post was not to imply that you don't know what you are doing, and doesn't have a snotty tone btw (no tone with the written word lol)
More that heavy stocking is for an advanced fish keeper, an advanced fish keeper would see an ammonia spike and not be surprised they would know how to respond and why it happened. A noob needs to stay with basic stock and for the most part stick to 1" of fish rule. When they get more advanced then they should play with the numbers.
I have had a long day with a very cranky kiddo so forgive me if I don't come off as a ray of sunshine.