Dying glofish tetras in newish tank

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Aquarium Advice Newbie
Jan 6, 2024
1~What type of fish is afflicted? In addition, please describe what is wrong with the fish to the best of your ability (i.e. cotton like growth, bloated, etc.). We purchased 3 glofish tetras 24 hours ago and this morning one was hanging out and hardly moving at the bottom, and died several hours later. There are 3 remaining that are moving around - though mostly at the bottom - and one of the 3 seems to be moving less in the last hour.
2~What are your tank parameters (ammonia, nitrites, nitrates, temp, pH)? Please give exact values.
Using Imagitarium 6 in 1 test strips:
  • Nitrate NO3 is 10
  • Nitrate NO2 is 0
  • Chlorine is 0
  • Hardness is between 150-300
  • Alkalinity 240
  • ph is 7.6

3~ How large is the tank? How long has the tank been set up? 15 gallon tank which was set up 12 days ago to cycle. I initially added Prime and Conditioner, added a used filter from my daughter's betta tank, a piece of spider wood and added 4 real plants to help get the water to the right levels. There is also a UV light.
4~What type of filtration are you using? Please give the name and number (i.e. Fluval 304) and amount of gph if known. Aqueon Medium Filter Quietflow Internal, 20 Gallon: https://www.petco.com/shop/en/petcostore/product/aqueon-medium-filter-quietflow-internal

5~How many fish are in the tank? What kinds of fish are they and what are their current sizes? 4 small glofish tetras
6~When is the last time you did a water change and vacuum the gravel? How often do you do this? How much water do you remove at a time? Never done it since it's new
7~How long have you had the fish? If the fish is new, how did you acclimate it/them? 24 hours. After the pet store tested the water and said it was safe, we got the fish and put sealed bag in the tank for 20 minutes. We then transfered the fish from the bag to a bowl with tank water using a net, and then dumped the bowl into the tank.
8~Have you added anything new to the tank--decor, new dechlorinator, new substrate, etc.? no
9~What kind of food have you been feeding your fish, have you changed their diet recently? We got glofish specific flakes. We've fed them a 4 times in the last 24 hours - very little.

Thanks in advance!


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You didnt cycle the tank.

What you did to start with, using some filter media from an established filter was beneficial. But those microbes responsible for the cycle that you introduced with the filter media need ammonia to consume and grow in numbers. With no ammonia source added for 12 days (your fish) those microbes will just starve and die. You either needed to add fish straight off and do whats called a fish in cycle, or dose ammonia and do a fishless cycle. Just circulating water with no ammonia in there doesnt do anything to cycle a tank.

Test strips are unreliable, you really cant trust anything they tell you. They also dont test for ammonia which is the most likely parameter to get elevated in a new aquarium.

You need to get a proper test kit, something that tests for pH, ammonia, nitrite and nitrate. API Freshwater master test kit is a good one to go for. Until you can properly test your water change 50% of the water daily. Once you get your test kit you can get on with cycling the tank.

Take a read through this thread and see the effects of adding fish into an uncycled tank.


Having said that, its unlikely that an uncycled tank is causing deaths on its own in 24 hours, although it wont be helping. Glofish are mass produced, inbred, GM modified fish and come with all sorts of genetic defects and health issues. Its not uncommon to have a number die just through the stress of moving to a new home and trying to acclimate to a new tank.
Thank you for the advice. So far 2 are still alive and the recommended test strips are on their way.
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