I'm a fan of potassium carbonate to raise KH - Seachem uses this in their product line
Aquavitro KH (link included for dosing information ... though must admit I have a bottle or 2 of the Aquavitro line
)
High levels of sodium (Na+) can also have less than wonderful effects depending on plant/livestock species - as in most things associated with fish & plant keeping, balance is key
I've read a lot about pH crash over the years but have never experienced it despite tap water with GH 1-2 & KH 0-1, pH usually runs ~ 6.5
Commercial systems are more prone to this effect re (very) high stocking density etc.
There are various natural water habitats that run pH 3 - 4 so it's not surprising that fish can do very well ... where the issue arises, is with introduction of new stock which will likely be coming from a system maintained ~pH 7 & suddenly placed in pH 3
Also fish coming from neutral or alkaline waters do tend to prefer these sorts of habitats (effects may be seen in unusual biochemical modifications, behaviour, sex of offspring etc)
Additionally there will be pH effects on the microflora/fauna living in the filter, substrate etc ... it's just a lot easier if you keep your tanks in the (expected) pH 6.5 - 7.5 range
so far I've added half a tea spoon of this BASIS WASSERPFLEGE Sunday and Last night, hopefully at the end of the week I should have the ph back to a normal level over a gradual period so not to shock the tank. The
sounds a good plan
I don't know how 3 buckets translates in terms of water changes, you want to aim for ~25% - 50% weekly water change; this will usually ensure that your tank conditions don't drift too far off your tap water parameters.
From what you've posted, you're definitely experiencing some issue with the tank (commiserations on the losses) so changing things up seems a good idea.