Consider moving Giant Danios to a longer tank. 3' at least. They may also munch your smaller fish. They get 4"
You should up your groups of smaller Danios. 6+. Are you able to sex by eye yet ?
For your tanks, you can mix Distilled or RO
water with tap to lower the PH. Stop using chemicals. Bouncing your parameters around is not good.
You can experiment with mixing distilled and tapwater to get the pH you want. Stable pH is more important than exact PH.
What will you do with the fry ? You should always have a plan before you breed fish.
You can add some of the offspring with the parents but you will need to add new bloodlines periodically.
Too much inbreeding causes deformities and susceptibility to illness.
Conditioning your fish before breeding, is important, good diet is important. Also you might add some live plants to help keep the water stable and give the fish more places to play.
Easy live plants are Java Ferns, you can tie them to rocks or wood , and they will grow in almost any light.
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