Advice Needed..fish Fry In A Under Cycling Tank

Hi,
I recently (around 4 weeks back) got myself a new tank. At that time I was totally unaware of the nitrogen cycle and the LFS guy too did not give me any information. On top of that he gave me around 18 fish and said they should be fine !!

I lost most of the fish within a couple of weeks. So I approached him and he said it must have been due to weather changes (the temperatures here had dropped drastically around that time) and advised me to install a heater. I believed him. As a gesture of goodwill he gave me a few more fish for free. However those fish too started dying one by one. So I started researching and came across fishlore and learnt about the nitrogen cycle and realised that I was inadvertently in the middle of a fish-in cycle.

I immediately ordered a API master test kit which just reached me today. However around 3 days back my last pair of fish (black mollies) passed away. I was planning to go ahead with fishless cycling but realised that before passing away one of the mollies seems to have given birth to around 8 fry !! I was elated but later panicked realising that the fry were in imminent danger. So I did a 50% water change to make sure that the babies were not affected by the ammonia/nitrites.

Today I finally received my testing kit and immediately tested the water. My readings are:

Ammonia : 0 ppm
Nitrites: 0 ppm
Nitrates: ~20 ppm
pH: ~7.5

I wanted some advice to see if this means that my tank has cycled and I can breathe easy? (Please note that presently my tank does not have any other fish apart from the 7 - 8 fry). Also any tips on how I should go forward taking care of the fry will prove invaluable.

Any help will be much appreciated.

Regards,
Sachin

 

It certainly appears your tank has cycled. You just need to feed them small enough food for them to ingest, and let them grow a bit before adding more adults so they aren't eaten. Feed them several small amounts, like 3-5 times a day. When you can add big fish again, you will have to go slowly, as your babies aren't a large bioload, and your good bacteria will need time to catch up to a larger bioload. Usually not more than 3-4 adults at a time. And Mollies are higher bioload than some species like tetras for instance. Congrats you have fish after all! By the way how big is your tank?

 

Thank you ! This is very helpful. I am currently feeding them a little pinch of finely powdered flakes every 3 hours from 9 am to 9pm. My tank is 108 lts (29 gallons). I plan to add a couple of swordtails after the fry grow big enough. Would that be ok (from a bioload perspective and also from the swordtails not attacking the young fry)?

By the way I have my thermostat set to 30 degC (86 degF), since before my old fish died I had noticed white spots on a few and thought that it must be ich infestation. I read that increasing the temperature is one to cure ich. Is it ok to maintain the temperature to this level (it has been at this level for the last 4 - 5 days), or is it too much for the fry? If it is ok how long should I maintain it at this level and then to what level should it be reduced to?

Thanks again for your advice.

Regards,
Sachin

 

I would definitely start easing temp back down by a degree each day. I don't think at this point it will kill them, but don't think it will do them any good either. The oxygen is depleted quicker in warmer water. Just do it by degrees daily to about 78. And check the site aquarium advisor for help on stocking tank once they are bigger. It's pretty cool, you can add in its calculator which species interested in with what you already have, and it will spit out info for you. You can play around with adding whatever you dream up, then take them off and start over. You can bookmark it when you are done as well. That being said, in my case I have a 30 gallon also, and I thought it was allowing too many fish. I don't want mine fully stocked. I added 7 zebra Danios to my original peaceful stock of 8 Pristella Tetras, and Danios were aggressive and chaotic, scared my fish and injured one pretty bad. I took them back to Petco. Catching them all wad a nightmare. Those are crazy fish Ive since read. I just have 8 Tetras and 4 Nerite snails, with 3 Amano shrimp now. All is well and my injured fish is healing. Tetras are spawning now, so they are comfy. I wouldn't get shrimp until you do research though. I have several posts on here about them and hard water, and doing reverse osmosis (RO) water changes at 10% to help soften water and help them be more comfy. They are fine now. I also didn't have enough cover on bottom of tank. Just a whole learning curve there. I love them now, but I was worried for couple of weeks. Good luck to you!

 

I'd feed a little less -more like 2 -3 times a day (and still only the tiniest amount or what you see them eat).
Wait til they're about 2 -3cm before adding swordtails (or other adult fish), even if they can't technically fit them in their mouth, they'll still chase them into a corner and harass / nip / potentially kill the fry (as when small, they're still seen as 'live food' by bigger fish). But mollies grow fairly fast, so shouldn't be too much of an issue. Good luck with them

 

Once they're about a half inch long or so, you'll need to determine their genders and how you're going to deal with the ratios.

I'm advising this for several reasons.

1. Mollies will breed with siblings and will start breeding very young (like less than 2 inches). So, if you don't want a lot more fry, you'll need to plan to separate the males and the females while they're still small. If you want more fry, you'll need to plan on a bigger tank or more tanks because a 30 gallon can't take much more than 8 adult mollies depending in breed and gender.

2. You'll need to watch your gender numbers and ratios or your mollies can accidentally kill each other. Mollies always establish a hierarchy within their genders. There will always be a dominant molly of each gender and dominant mollies love to show off that they're the boss to others of their gender. If you only have 2 males or 2 females, the dominant one can pick on the subordinate one so much that the subordinate one will die of stress. So, for genders, it's best to have either 1 of a gender or at least 3 so the dominant molly can split its attention between the 2 or more subordinates which gives each subordinate molly a break from the stress.

If you're going to keep the males and females together, you'll need a ratio of at least 3 females for each male. This is because male mollies have have a desperate need to reproduce. If there is only 1 female for a male, he will hound her relentlessly and can make her so stressed she will die from it. So you have to have enough females for each male that he spreads his attention around.

Worse, though, is if you have more males than females in a tank. The males will fight over the females if there isn't enough females to go around. If the males fight, being brothers won't stop them from wounding and even killing each other.

So, have fun with the fry but it would be a good idea to start sexing them and planning the logistics of how you're going to manage them, (either by getting a second tank or planning on getting more of a gender if necessary) as soon as possible.

 

Once they're about a half inch long or so, you'll need to determine their genders and how you're going to deal with the ratios.

I'm advising this for several reasons.

1. Mollies will breed with siblings and will start breeding very young (like less than 2 inches). So, if you don't want a lot more fry, you'll need to plan to separate the males and the females while they're still small. If you want more fry, you'll need to plan on a bigger tank or more tanks because a 30 gallon can't take much more than 8 adult mollies depending in breed and gender.

2. You'll need to watch your gender numbers and ratios or your mollies can accidentally kill each other. Mollies always establish a hierarchy within their genders. There will always be a dominant molly of each gender and dominant mollies love to show off that they're the boss to others of their gender. If you only have 2 males or 2 females, the dominant one can pick on the subordinate one so much that the subordinate one will die of stress. So, for genders, it's best to have either 1 of a gender or at least 3 so the dominant molly can split its attention between the 2 or more subordinates which gives each subordinate molly a break from the stress.

If you're going to keep the males and females together, you'll need a ratio of at least 3 females for each male. This is because male mollies have have a desperate need to reproduce. If there is only 1 female for a male, he will hound her relentlessly and can make her so stressed she will die from it. So you have to have enough females for each male that he spreads his attention around.

Worse, though, is if you have more males than females in a tank. The males will fight over the females if there isn't enough females to go around. If the males fight, being brothers won't stop them from wounding and even killing each other.

So, have fun with the fry but it would be a good idea to start sexing them and planning the logistics of how you're going to manage them, (either by getting a second tank or planning on getting more of a gender if necessary) as soon as possible.

Just thought I'd add a few things to this:
I find ratios don't really matter much with siblings, the males chasing/stressing females out usually happens more with unrelated fish or fish that didn't grow up together in the same tank (or when adding new fish) -for me at least, I've never had an issue when they've grown up together (mollies/swordtails/platys).
If you don't want lots of fry, you can also simply just keep the water cooler and they'll only breed on occasion (eg. unheated indoor tank if your house doesn't get overly cold, or set the heater to a lower temp). I find I only get fry if I want fry (and use a breeding trap), as the fry would otherwise just get eaten or sucked up into my filter -so there's always that too. Mollies don't always eat all their fry, but swordtails almost always will, so adding a few species will take care of that too.

Healthy fish in the top hierarchy will almost always kill a sick/weak fish if there is one, but if they're picking on other healthy fish then you need to adjust your ratios (typically with livebearers it's 1 male to 3 females).

Having said that though, I've occasionally had the odd fish that is just a rogue terror -surprisingly always female. If you happen to get one like that that's just a total pain, it's best to remove and rehome it ASAP.