Hello. I apologize about the length of this post. This is my first one, so hopefully I get everything that is needed. We have a planted 20 gal tank that has been running for about 7 months. We have had fish in it for 5 months. We have 5 panda corys (since the beginning), 1 honey Gourami (and 3 weeks), and several cherry shrimp (count unknown as they have been breeding). There are some bladder snails and ramshorn snails as well. We have a 20 gal HOB filter, an AQQA AQ-016 internal filter ( we were planning on pea puffers initially), and an air stone.
My husband and I wanted a schooling fish to make this a true community tank. We initially tried 6 rummy nose tetras, but they immediately started dying off. We had one that survived, so we attempted to reintroduce a group. Eventually they all passed.
We let the tank continue for roughly over a month before we introduced a group of green neon rasboras. We acclimated them by floating the bag and adding tank water every 15ish minutes for 45 min before adding them to the tank. Within 72 hours, the school was gone. At this point, we checked gh/kh. Gh 200 was and kh was 50. We were concerned this might be the problem and used a water pillow and started using more distilled water during our water changes. The gh was 120 and the kh was 100 after two weeks.
We tried again with a school of green neon rasboras and a honey gourami. We acclimated with a drip system and slowed the process down in case we were causing shock with our previous attempts. We also used the paraclense, ich-x, and erythromycin combo on the entire tank for prophylaxis. Just as before, the rasboras were gone within 96 hours. Outside of one that seemed incredibly stressed, all were schooling in the middle of the tank and eating well. They just started dropping one by one. The gourami (and our 5 pandas) thrived.
At this point, my husband and I went to our LFS to see if we were missing something. They recommended checking pH when lights came on and off to see if there was a massive ph swing. Lights on - ph 6.9, lights off - ph 7.1. Our LFS suggested black neon tetras, citing they are hardier than most. We did some research, waited a few weeks to get our gourami fully established, and tried a group of 6. They had been quarantined at our LFS for a week. We acclimated them as our LFS recommended: float the bag and add some tank water every five minutes for every 0.1 degree of ph. This was done 2 days ago. As of now, we have only one tetra alive.
Recent weekly stat range:
ammonia 0
nitrite 0 - 0.125
nitrate 10 - 30
pH 6.8 - 7.2
My husband and I are so incredibly frustrated. I have looked at countless sites online and cannot see what we are doing wrong. I am not going to bring fish home just to die and already feel like I have done that. Unless someone has anything else we can try, this tank seems like it will just be for our gourami and corys. Thank you for anything anyone can provide.
