Sour dough bread

We have been baking our own bread for a while now.  Shop brought bread never tastes as good now. We had been baking spelt loaves with shop bought packet yeast but I recently had another go at sourdough.  We buy lots of things in bulk from essential food coop, big bags of flour being one.  We thought we would try rye sourdough next as the flour costs less.  But I think it is an epic fail. Our loaves of sourdough tend to rise beautifully especially in the heat wave we are having at the moment.  But today is the first loaf of a hefty 25kg bag of rye flour and it is looking flat and pathetic...what will the children say! They have only just got half used to the acquired taste of sourdough! And are once again eating some lunch! Poor bunnies, how do they put up with their experimental mother...I think the recipe for rye sourdough must be different from my spelt one.  Ooops!