At minimum, bumping up the GH to 7 may help.... and striving for an algae/vegetable based diet with a protein source as a secondary option...
What I mean is.... read the labels! Many "algae foods" are actually algae infused and don't have algae until the 5th to 9th ingredient. Algae or vegetables should be the primary ingredient. This is to be fed twice a week.
Then you can use a meat based food once a week.
If you can do those two changes and let us know the results in a few weeks that would be great!
You can work on upping the GH slowly through water changes or faster.
As for neos in low pH.... I've got one that's been living in "waste water" from my main tank that's tested below 6 pH. Doesn't have any substrate in the container... and I just added some fresh neo blood into the main tank to see how well they'd do. One of the shrimp that was added is a berried female. KH is at 0.