I'm approximately 25 days into feeding my Tartine starter (every 24 hours - 150g flour mix, 150g water, 75g starter).   The starter was residing on my kitchen counter (approx. 69 degrees).

Last night I progressed to making the Leaven (1 Tbs. of the starter mixture, 200g flour mix, 200g water).  This morning I did the float test and it sunk.  I then waited 30 minutes (placing the mixture in a warmer place) and the mxiture failed the float test again.

Finally I mixed half the starter mixture, 100g of flour mixture, and 100g of water.  Let it ferment for two hours and again the dough didn't float.

I have not had an extreme amount of bubbles at any phase.  The rise/fall has been subtle.  The aroma is sweet with a hint of acidity.

Thank you for any advice.  I have NO idea what to do next.