Just Need Some Advice...

[PandaGeneral]

Okay so i am new here, created an account so i could get some insight on something my fish has been doing for a couple days now. I have 2 Mollies, and 4 Neon Tetras in a 29 gallon tank, its been cycled for 6 months and i have had no major issues with it. I started out with the Tetras since they are hardy and i wanted to use them for cycling. Anyways, I've been checking my water and doing my weekly 20% water changes, with it being 6 months i actually took out about 40% a couple weeks ago. Everything has been pretty good, but my question is did i mess up the cycle by taking out so much water? My mollies are like swimming up and down the sides and front of the tank, but the neon tetras are completely normal and schooling with each other.  i checked my water perimeters and every thing is in order as far as i can tell, ammonia 0 nitrite 0 and nitrate was 10ppm. which all seemed normal to me. Anyways is there something wrong or is this pretty normal behavior? the mollies are completely new to me and there are only about 15 babies in the tank, she was prego when i got her, so i don't think its an overcrowding issue. Just wanted to see if its something i should be concerned with or if i am doing something wrong 

 

[the_lock_man]

No, you didn't mess up the cycle. That is for sure. Very very few bacteria live in the water, they live on surfaces, primarily but not exclusively in the filter, also on decor, substrate, etc.
 
A few questions and pointers
 
You aren't overstocked now, but when the fry have grown somewhat, it will be incredibly overcrowded. How long have you had the mollies? It may just be that they are still settling in, if you have only had them a day or two. How hard is your water? Mollies are from hard water, and they need a certain amount of calcium to be healthy. They also need a little salt in the water (which the tetras definitely don't), so you may find that they don't last wonderfully long - that's certainly what happened to me when I kept them. Swimming up and down the glass is often a sign of stress - it could also be that they can see their own reflection in the glass and don't realise it's them, and are getting a bit angry at their own reflection. This can happen with bettas and gouramis.

 

[PandaGeneral]

Thank you for the detailed answer, i have had the one that is swimming against the glass the shortest amount of time, she's been in there for about 2 days, my other female has been in there the longer. I have another tank that i am in the process of getting a stand for that will house all the babies once i get it up and running, they will then be going to a LFS that i have already arranged. So hopefully i get that setup soon. I actually noticed today the fish in question was only doing it this morning, once i fed her she calmed down and hasn't done it since. So i think you were right about the settling in. Also i do have some salt in there, again i had my LFS help me out with how much to add and all that jazz. They said the same about the tetras but said it should be fine. Thank you again, i will take your advice and see if it starts back up. Lets hope it doesn't! Have a great day!
 
Oh and my PH is about 7 right now, i know the mollies like it higher and the tetras like it lower, but when i get the other tank setup i plan on moving the mollies, so hopefully everyone will be good until then. I should mention, in my original post i made it sound like both mollies were exhibiting this behavior, i didn't mean it that way, its only the one that i introduced a couple days ago that was doing it. i just wanted some insight since i didn't see or notice it when i got my first molly. 

 

[the_lock_man]

I would disagree about the tetras being fine with salt in their water. They will probably be fine in a high pH, but the sooner you can get the mollies out into their separate tank, and keep the tetras in completely freshwater, the better.

 

[PandaGeneral]

Well its barely any salt, probably just enough to help with gill function and so on and its freshwater aquarium salt. Not Marine salt. its been about 2 months since they were introduced to salt and i haven't lost any. They may not last as long but they seem to be just fine. Eventually i will separate them all but for now i just don't have that option.  the swimming against the glass is all gone today, she has been fine since the lights turned on this morning. Thanks for the help! is there a way to mark this as closed?

 

[mhancock]

Just wondering  - did you use chlorinated or treated water?  Whilst a 20% water change can be done with untreated tap water, I believe that 30% is the maximum so 40% may have killed some of the bacteria in the media and started a mini cycle which some of the more sensitive fish could have been affected by?  

 

[Byron]

On the salt, you should not be adding it.  You may not see the problem in the fish, but it is still there internally, and it is seriously weakening the neon tetras.  Characins have no tolerance for salt long-term.  It affects their physiology and weakens them.  As for the molly, while salt will not harm them, it is not essential.  So here with both fish together I would certainly not use it.  
 
Once the mollies are on their own--and by the way, they need space as they do get large--they need harder water (no mention is made of the GH and this is the crucial thing when one is dealing with soft/hard water fish, more-so than pH) and salt is up to you.  Marine salt would then be better as it contains the other minerals which are crucial to the health of mollies.  The salt is not the issue but it won't hurt.
 
Byron.