I mixed the second batch with distilled water, and used that to dilute 1+1, let it sit for 30 minutes before using. Test strip came out perfect with boosted contrast as to be expected from increasing the times. Used tap water to mix 1+1 as an experiment, let it sit for 30 minutes and then tried it. Thin negatives from a second test were the result. Not as thin as the botched ones but the sprocket numbers were thinner than they should be, as were the images. I used the same time as i had for the botched rolls for both these tests. I always do a test before anything mission critical anyway, so all that got lost was developer and a couple of test rolls, not anything crucial! A bummer at £10 a packet but hard lesson learned. I tested with filtered water, that test strip came out fine as well. I wonder what it is in the tap water that harmed XTOL but has allowed me to use C41, E6, RA4 and many other film developers without a problem. The test negatives from the under developed ones were printable, and the first ones printed nicely as well, it seems a bit sharper than D76 at 1+1 or is it just my eyes? I mixed this batch more gently as well. I will be mixing all chemicals from filtered or distilled water from this point.