General rule is an inch of fish per gallon, and you want your sorority tank heavily planted and decorated to give lots of hiding spots...so I'd think you'd be fine with around 10? Though I wouldn't put all in at once!
Being over eager, when I started mine, I let myself be talked into putting 7 in together with insufficient time to adjust, and it didn't go well. Two died, two had to be removed. The three that were left have done well, and I've SLOWLY worked additional girls in, so I'm back up to 7 that all appear healthy and are getting along well together. One of the two removed will be ready to return soon. The other will get a permanent BFF and home in the form of my dwarf frog and the 5G tank I'll be upgrading him to this weekend.
Moral of the story? Take it slow. It still might not start off well. Be prepared to have to QT or isolate some temporarily. Be prepared to house some outside of the sorority tank permanently (or find them new owners) if there are significant issues. But with patience and a little luck, you'll have a tank full of colorful fishy jewels!
What size tank do you have?
I've got my 10 gallon set up almost (besides the cycle) and I have three of my girls, all in one gallon QT/temporary tanks until I get my other girls and QT them. I think I am going to get three more... so 6 total in a ten gallon. I'm waiting for my fishless cycle to complete and it's taken longer than a month, now. :/ I DO NOT want to start a sorority in an uncycled tank!
I am going to float them all beside each other so they get used to each other (to QT them when I get my new girls)... My current three already know each other quite well. They try to "attack" each other through the glass occasionally, but it only lasts for 1/2 a second now, and then they just swim off.
I also have an empty four gallon back up tank (it has a filter and decor, but no fish). I'm really hoping that my sorority will work out... I don't want to do anything wrong. I hope I've got everything planned out thoroughly enough and that my cycle will be able to handle six fish at once (definitely planning on daily testing and PWCs when I first set it up, wouldn't want to stress them even more!)
I've now been introducing the *NEW* new girls to the tank by putting them back in their cups and floating those for a couple of days (with lots of gradual water adjustments) so that they can see the tank and other girls, get used to the water, and the other girls can see them and get used to them. The last one I let go, Wraith, was probably wierded out when I submerged her cup and (I kid you not) 4 of the other girls swam INTO it! Probably just to make sure she wasn't hiding any food in there
So far there's been a little chasing, and I had to time-out Christmas for a day when #4 and #5 were released. But overall, they've been very good girls!
The tank was not fully cycled, but I stuffed a LOT of plants into it and I've been watching the parameters carefully. (Side note, the Water Wisteria is going nuts in a good way, instead of slowly perishing like previous ones put into the small unfiltered tanks did)
Well I have the lighting and Seachem Flourish for the tank but no live plants. You think it would be good to add the live plants before I add the girls? I'm not sure where I'm going to get the plants yet and I've never had live plants so I'm unsure if I can keep them alive. My tank has an abundance of silk plants so the live plants would have time to grow without the girls having little cover.
Can I ask where you got your girls (private breeder vs pet store) how long you QTed them and if they were siblings/from separate breeders, age, etc...? I want to do everything right because I don't want to end up with dead/fighting girls and have to rehome them (this would NOT be easy in my area!)
I'm pretty sure I started off wrong, as the above tale relates! I'm trying to do it right(er) going forward though.
Yes, put live plants in first. I got mine though chain stores - Petco and Petsmart. They typically have plants in tubes (do not buy before confirming the plant in the tube is an actual fully submersible water plant - not all of them are!) and normally an aquarium or two dedicated to live plants. I usually buy from the tanks, though I have gotten a few in tubes. I take my smartphone with me and look up the kind of plant it is on the internet to verify it is a aquatic plant. I don't have a NPT. I just stick em in the gravel. Some easy to care for ones: Amazonian Swords (will get pretty big), Banana plants, Marimo Moss balls. Wash them well and you should QT them too - plants are certainly a vector for unexpected things to get in your tank. Mostly wee snails.
My girls are pet store mutts. I just would plain be terrified of having live girls shipped to me, so even though this site has lots of breeders and lovely fish...I would not feel comfortable risking it. Hubby and I both work, so there would be every chance that anything delivered would be sitting outside of our house for 4-6 hours. I got some Nerites off ebay last year, and they happened to arrive on the hottest day of the year. One of them was already gone by the time I got home and rushed them inside. Anyway...my girls - the initial 7 were purchased together at petco and judging from the range of colors and tails are unrelated. I *HAVE* read that sibling girls will tend to do better in a sorority, so since you have sibs, you are probably starting from a good spot. If a fish is sickly looking when purchased or upon arrival, keep it separate until it is returned to health. The healthy looking ones go into the tank within a week, and I float them in their cups in the tank for two days to acclimate them to the other girls and water. (This is a fun time, the girls in the tank have thus far been super curious about the new arrivals!)
But fwiw, this is not ideal. I should QT them longer - many do it for up to two weeks, but I work, hubby works, and with kids, cats, and afterschool/work activities for everyone, I am eager to get them into the tank where they become much easier to take care of. I have my full arsenal of medications standing by (and thanks to the tetras, we've already fended off one bout of Ich) in case of emergency. Keeping the water in good shape is the first line of defense, and the plants help there.
It's *excellent* that you are doing it right, and I imagine you'll have great success! I got off to a wrong start in many ways, but it is still going pretty well at THIS point.