I have a 10g tall with 1 guppy and 3 neon tetras. How many more fish can I add? I am thinking about 1 more guppy and 3 more tetras. The aquarium is 16" tall and 12" wide and 12" long
1. They are all males and I plan to get more malesOoooo. Be careful. Guppies are livebearers and breed like crazy once they get going. You also need a 1:3 / 1:2 male to female ratio to keep them from getting stressed. Two female guppies would be perfectly fine. Two males.....it's ify, but my guppies do very well together, even the males. They can get a little territorial and nip at each other's fins. Tetras are also schooling fish and they like the middle section of tanks. So here what I think. Get another guppy, preferably the same sex, and add no more than 4 tetras. Or, get a bunch of guppies and add like 1 or 2 more tetras. Also two questions.
1. What gender is your current guppy?
2. Can you include a picture?
Best of luck!

Yes it has been cycled.Questions that need answers...
Has your tank been cycled?
What is the nitrate levels?
How often do you change water?
As long as your tank is cycled and you’re willing to do weekly water changes of 30-45% Then you could safely add maybe 3-5 neon tetras with a single guppy or 2 guppies with 1-2 neon tetras. I highly recommend you get 2 amano shrimp, 2 tetras, and a single guppy. This way the substrate can be clean and you can have something roaming the bottom. Best of luck!
Super cute, and no worries, been there done that. Definitely a good tank for those tetras nad guppies, they're color will really pop in there.1. They are all males and I plan to get more males
2. Here's a picture. Sorry for quality. I'm taking the picture from my Chromebook camera because I don't know where my phone isView attachment 757616
Yes it has been cycled.
I don't know the nitrates currently but they are always low because I have a few plants
I change 1.5 gallons every week. Should I change more?