Rapid PH changes at WC and shrimp behaviour

I am considering switching to larger weekly water changes in my 300l tank (from 30% to 50%) by adding more tap water to the mixture. I am currently using a 2:1 ratio of RO to tap water, and planning to get to 1:1. There is a problem, however, with a large pH difference between the tank and the new water. The water in my tank is 6.6 pH (the substrate is ADA Amazonia I). My tap water is 7.6-8.0. The water mixture I would be adding to the water column would be about 7.5. That is almost 1 grade in pH scale, which (since the scale is logarythmic) changes the water acidity ten fold. It's enough to shock more sensitive shrimps.

So here's the question: what are your experiences with shrimp behaviour on the water change. How do your tap waters differ from the tank water as regards pH? have you had some major deaths because of the sudden pH change on the WC day? Any way to avoid it without reaching for pH decreasing chemicals?

 

Tom, have you had any observations on sudden kH changes and shrimp behaviour? My tank water is at 6 kH, while my tap water is at 11 kH. With 1:1 mixture of tap to RO the difference should not be that large (since RO water is around 0 kH). But I have no idea how much of a difference would be too much for inverts.

Still, your comment made me realise that theoretically changes of tank water for pure RO could be stressful to shrimps, considering the kH difference (with RO being at 0 kH, and tank water certainly higher for all the Mg and Ca from ferts).

Any comments on the buffering ability of an average well fertilised tank water at the point of receiving pure R0 water? Or is that too unpredictable for all the possible variables? I know with fish and plants it does not really matter much, but with shimps it might (as anyone who had sudden mass shrimp deaths would know).

Oh, and by the way - is there any target, optimal water hardness level in EI method? I don't think I have seen this addressed anywhere.