Need Help with Starter

i think soupy with bubbles is fine!  Maybe don't give up and start over. How come you stopped removing after 3rd feed?

I just recently started by sourdough starter adventure since I ran out of instant yeast in this quarantine so I am by no means an expert, just sharing what worked for me. I used Josua Weissman's recipe which calls for 50g of rye flour and 50g of unbleached AP  flour. I was unable to find bread flour or rye flour so I exclusively us unbleached AP and filtered water. But I will write out the recipe as he has it. 

Day 1: 50g rye flour, 50g unbleached AP flour, 150g water at 85degreesF

Day 2: 70g mature starter, 50g rye flour, 50g unbleached AP flour, 115g water at 85degreesF

Day 3: 70g mature starter, 50g rye flour, 50g unbleached AP flour, 115g water at 85degreesF (same as Day 2)

Day 4: 70g mature starter, 50g rye flour, 50g unbleached AP flour, 100g water at 85degreesF

Day 5: 70g mature starter, 50g rye flour, 50g unbleached AP flour, 100g water at 85degreesF (same as Day 4)

Day 6: 50g mature starter, 50g rye flour, 50g unbleached AP flour, 100g water at 85degreesF

Day 7 (and beyond): 25g mature starter, 50g rye flour, 50g unbleached AP flour, 100g water room temp

I was stressing because I wasn't mixing flours but this has been going strong for over 3 months now. I hope this works for you! Good luck!

I feel your pain. I gave up my first one after 2 weeks or so. But I just had to do it again. So I just kept on feeling my second one even if I didn't see much happening. In my case, with my cold kitchen during winter (63-65F), it took me 7 weeks or so until I reached a very active starter that doubles in 3-4 hours even in colder temps. Just keep going!!

You do not need to keep such a large amount of starter unless you want to.  The ratio is what is important.  For example, at the day 2 feeding, you had 200g starter.  You removed 100g (keeping 100g), and added 100g water and 100g flour.  So you used starter, and water, and flour all in equal amounts.  On this forum, many people would write that as 1:1:1 to indicate 1 part of each.  Your starter doesn't really care if it's 5g or each or 500g of each, as long as each gram of starter gets fed an appropriate amount.

Do you have any idea what temp your starter is when using the propagation mat?  You need to be sure it's not too warm.  You need a lower temp to get yeast to start growing (somewhere around 75F I think but I'd have to go digging to be sure).  Many people think warmer is better because we use 85F to get them to rise dough faster, but it's different to get the yeast to start growing in the first place.

Having your starter turn liquidy is a sign that it is getting more acidic.  In the very early stages of your starter's life, this is a good thing because the low pH kills off unwanted organisms and encourages the right ones to move in.  It seems like maybe you are throwing out your starter attempts just when they are on the verge of turning into viable starters.  Later on, you don't want it to get too acidic because it'll affect your baking by dissolving the gluten (that's why it turns so liquidy) but for right now it's a good thing.

Read the following excellent article for more information on what is going on in your starter at the microbial level.   Be sure to follow the link at the end to read part 2:

http://www.thefreshloaf.com/node/10856/pineapple-juice-solution-part-1