Are your pH readings from a de-gassed water sample since you are using CO2.
As others have said seems like ammonia content is the problem.
Does a cycle stall without enough NH3, sure it will.
With that low of pH total ammonia reading are almost all NH4.
Does BB process NH4, I am unsure, someone will chime in.
I doubt it since there are complaints of cycling a low pH tank.
IMO raise KH by adding CaCO3 to about 2-3 dKH.
CaCO3 is not very soluble but in low pH it will dissolve.
Another alternative would be CaSO4(gypsum) food grade from a brew store, dissolves a little better.
Both of these will make a white cloud for about 6 hours to raise 2 dKH.
Reduce CO2 output to half of what you use now.
Raise pH to 7.2 to 7.5 and complete cycle first.
Once cycled you adjust total water hardness with WC's.
KH test kit for very low KH.
Use 10ml sample each drop is .5 dKH
Use 20ml sample each drop is .25 dKH
If 1 drop in 20ml doesn't show a light blue hue, don't bother wasting drops.
Do you know the GH of your tank water?
That can be raised with MgSO4.7H2O(epsom salt/magnesium sulfate)
This stuff dissolves quite readily without clouding.
I only mention these compounds since they are cheap and locally available in most places.
$3 to $5 per pound is typical.
Note of caution: when you raise the pH your water will become more toxic (NH4 back to NH3) to your existing livestock.
These large alkalinity changes are also not easy on livestock.
Regarding ICH: Could be possible that ammonia stressed fish are more susceptible to many illnesses.
If this water is from the tap it may need to be always mineralized depending on livestock choices.
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Growing is not that difficult.