I found this interesting!

[Thyra]

My grandson left for college and his Mom (my daughter) wants me to take the two angel fish. They have had them over 4 years and they are approximately palm size in a 30 g tank. I don’t have the room, but I asked her about their care. I have seen the tank over the years and it was always clean, no live plants and very little decor. At the time I didn’t have my own tanks so I didn’t pay a lot of attention to the fish. They have had the tank for 11 years with an underground filter. They have never removed the gravel or the filter. They have never added any dechlorinator or any chemical of any kind - just city water from the faucet. She adds water as it evaporates, and they “clean” the tank every couple of months. There are a couple of other fish in there, but she doesn’t know what kind and I haven’t seen the tank since I got involved with my fish about 4 months ago. Even if I had the room, I’m afraid to take the tank because I might break the cycle. lol

 

[aakaakaak]

If you keep the filter media and the gravel you should be able to keep the cycle. If you took the water with you in jugs you could probably do even better with the cycle.

Even though the conditions they've been in have probably been pretty bad it doesn't mean you need to keep them in those conditions. Just remember to change things gradually.

 

[Newman]

just treat it like a normal fish tank and do what aak said, gradual change to w/e method of tank keeping you feel is right.

 

[Thyra]

I really don't have room for another tank and my tanks don't have room for those 2 fish. The other thing that bothers me is even when my kids were still at home and we had the aquarium, we never managed to keep angel fish long enough for them to grow. I don't know if it was us or the fact that our well water has pH in the 8s and I am not about to start messing around with pH.

 

[Newman]

you know I am curious about the same thing. my tank's normal pH was around 8-8.1pH. I say "was" because once i added my CO2 system, I made sure the pH went down to exactly 7pH (just because with my parameters this means 25 ppm of dissolved CO2 which is good for plants). I realize that the pH altered by the CO2 injection is not entirely the real pH of the tank, but I have been wondering if I could keep Angelfish in my tank now...of course I have no opportunity to try them because I already chose sailfin mollies instead of angels, but it was a thought.

 

[Thyra]

Tell me about your sailfin mollies. I just lost two with what I am positive was swim bladder. I have just been feeding them regular food and occasionally freeze dried blood worms - and not soaking them or whatever you are suppose to do. They both had the same pattern - first kind of swimming with their tails sort of down and then advancing to a nose up vertical position - they did not appear bloated and I examined them after they died and found no apparent ich or injury. They eventually - when they moved - would flip, flop and spin. I like mollies and have three in my other tank and would like to get more. I do not want to use salt, though - at least I don't think I do. That is another thing that appears controversial.

 

[Newman]

I'll tell you about the way i am housing my mollies right now. Be aware that i have had them only for a short time, having sold off my swordtail/platy about 3 weeks ago and having acquired these mollies at that same time.
What I have are wild mollies, claimed to be sailfins. they were collected in full freshwater in a river inlet in Florida. thus I can see they are adapted to the FW environment. Since I commonly read that mollies do best with some salt in the water, I had to somehow implement salt into my tank in some way as to not harm my cherry shrimp, otocinclus/corydoras catfish or my plants. What I do for now is I put 1 teaspoon of instant ocean salt into my tank water for every 10 gallons of water. So far I find it has little effect on my plants and animal livestock. I see the Specific Gravity of the water is somewhere around 1.002 which is very low, but i guess some presence of salt in the water should make the mollies happy. They sure seem ok to me so far. The females seem to be young for the most part, but the most mature one has already dropped fry a few weeks ago and i suspect is due to drop within the next week again.

I feed them 6 days out of 7 every week. 1 day is to get their systems cleansed so i do not feed. I feed them Spirulina 20 flakes every morning and I will sometimes give them so sort of other food in the evening. They love frozen bloodworms, Freeze dried tubifex cubes, shrimp pellets, freeze dried brine shrimp(didnt offer my frozen kind yet but im sure they'll approve), and to some degree they also take freeze dried bloodworms.
I am going to see if they will accept some of my Formula One flakes that i feed to my clownfish too, just to add to their variety, and I suppose i should introduce them to green peas soon

With regards to my water, I do a water change once every week, changing out 5 gallons, i make sure to add 1/2 teaspoon of the salt. Tank temp stays around 77F. pH is around 7pH due to CO2 injection. KH value is 8-9dKH, GH values are massive, 25-30dGH.
I top off with RODI water just like in my SW tanks.

And that is what i do with regard to my mollies. Idk how it will work out in the long run, but of course I update my 40 gal journal (in the rate my tank section of this forum) frequently, so you will know if something is or isnt working out

It is unfortunate that your mollies felt sick, perhaps you are not keeping them in alkaline water?