Help guys! Failed leaven float test.

Hey, 

So I have been following this website closely to modify my process but I have come across my first road bump so I figured I'll write a post to see where I went wrong and hopefully rectify that.

So for starters I am trying the tartine bread basic country loaf. And my environment, I live in Karachi Pakistan where the ambient temperature has been aroun 30degree Celsius(86 f) and around 78% humidity. 

Now when I started I made a mistake and mixed water with 50/50 whole wheat and ap flour blend. Left it in my basement for 2 days and 2 days later I had some hootch on top. The hootch I poured out and fed my starter with 1:2:2 ratio(Starter:flour:water at room temperature) the flour I started using in feedings was 50/50 wholewheat and bread flour now. 

I feed it once a day around mid day. By 9 pm the starter is at its peak of activity and almost doubles in size. Definitely a 70% increase. I have been feeding t for 2 weeks now. 

Today I had assigned the day for making my bread. So last night around 2 am I started my leaven so 1 tbsp starter, 200grams flour blend(ww and bread) and 200 grams water. Now the book asked for it to be kept at 68f which is impossible to achieve here. An airconditioned room is around 75f and the fridge is far too cold. So I decided to use chilled water for my leaven (is this where I went wrong?) and I left my starter in an air conditioned room. 

After about 12 hours (2pm) I was ready to do the dreaded float test. Now my leaven had risen around 5% and was still cool to touch I tried it anyway. It sank. 

I decided to leave it for a couple of hours and come back to it. I left it In a warmer environment so on top the fridge. And left it there for another 4 hours. it had risen about 50% now but it still didn't pass the float test. 

Now i am away for th day so I have fed it again 75gms starter 150gms flour blend 150 gms water. I'll come back in about 24 hours and fixing the feeding schedule again and then try again. 

i know this is long. Apologies. I just feel confused because its so hot and humid here I feel like I should be doing something differently. 

Guide me fellow bread lovers!