I rallydont know but I think that EI dosing with that low KH not is a good idea dosing it at full strengh once.I think you can dose the fertilizers parcially, dose it every day, just divide the dosing by 7. small doses dont alter things a lot. by the end of the week you will have lower pH but because it downs slowly your fish can aclimate. Still your pH maybe dont change a lot because your plants sucking nutrients will affect pH so it can neutralize the Phos effect. Another thing you can do is mantain the pH low with the ferts. Just when do w/c mix the ferts (Macros) with the new water in a bucket so the pH will be the same as the pH of the aquarium, so mantaining lower pH with Macros.