Stocking for a 20 gallon high


I’m looking to rescape my tank, and once that’s done, add more fish. I just wanna know how many fish I can add and what fish. I currently own a 20 gallon high with these fish:

4 platies
3 swordtails

How many more platies can I add? I want to add a male tuxedo platy and some more females to the tank. Is there a chance I could add Cories as well? I feel like that would be pushing it but I love cory cats and don’t have the space to set up a tank for them. Also, with the stock, how often should I do water changes? I currently do 10-25% water changes weekly and filter cleaning monthly.


Are the platies and swords that you already have male or female? I would not attempt to add mixed-sex swords or platies, your tank does not have room for the females to escape when they are exhausted from being chased by the males all day and all night. And you will be overstocked in a month.

You can add a school of 6-8 dwarf cories or 8-12 pygmy cories. I strongly urge you to get a dwarf or pygmy species and not a larger species.

I would not add more platies or swords if you want to add a school of cories. The swordtails get surprising large, and you may even consider rehoming them,

I would suggest that you do larger 30-50% water changes. You may not need to clean the filter that often, Make sure that you don't clean the entire filter the same day as a water change. You can rinse the cartridge in tank water one week, and wipe the filter walls the next week.


My platies and swordtails are mixed, I have 2 males (swordtail and a platy). I’ve had them for a while and fry is not much of a problem, since they just eat it before I can even catch the fry. If any fry do survive though, I do have a 5 gallon tank that isn’t set up, but it’s small enough I should be able to grow them until I can rehome them. The males don’t stress out the females too much and there is plenty of places for them to hide if that’s the case.

I’ll look into dwarf/Pygmy cories, but if I don’t choose to get them, how many more platies can I add?

also, I understand that swordtails get big. My local fish store has a tank labeled “assorted platies” so I asked for any of the platies in the tank. I got a Mickey Mouse platy and a male and female swordtail. Went home and realized that two fish looked different than my other platies, and researched to find out they are swordtails, and get big. So I kept the swordtails and bought another female so the original female wouldn’t get stressed out, and here we are today.

Thanks for the advice on cleaning, I’ll be doing that now! This was very helpful.


stick to one or the other. Swords and platies can interbreed. and you aren't doing the fish any favors by facilitating that to happen. Whats the point of bothering with tuxedo or mickey mouse when you're going to likely create mutts anyways? Just saying..l

Add the cories, they'll mostly stay low. then pick one or the other to work on. swords or platies. and stick to that single species. 6 or 8 cories, 6 or 8 platies or swords. should be fine in a 20g.

same routine on water changes, except test for nitrates, if you see it gets into 20-40ppm range, step up the water change either by doing it more frequent or a bigger change at the same frequency.
main point it to remove what the tank is producing during that time, and a little more in order to keep them from building up out of control. your bacteria and cycle will size up to the new fish demand. just you might want to add 6 or 8 cories, wait a couple days and get 3-5 more platies.


Ok thank you so much!

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