Hi tomhog,
Your title indicates as using SWC & post says top fertilizing.
If you are also putting fertilizer in the SWC reservoir, or have a controlled release fertilizer strip in place it may be excessive.
In case you are only top fertilizing then it still can be excessive. The well balanced fertilizer for in ground use is not always benign to pH in a closed system.
The pH can make nutrients that are given to the plant go awry. You are quite probably not lacking nutrients, but rather "locking" out nutrients.
First place to review is the % of urea & ammonia forms of nitrogen that you have been using. If you loaded up on more than 15% of those then flush the growing medium with only water to try & get a fresh start.

I am not putting fertilizer in the reservior. I started out using a balanced fertilizer which I mixed into the mix when I first planted and 'side dressed' when the plants set fruit. I have since supplemented every 2 weeks with a foiliar feeding of diliuted seaweed / fish emulsion.

Thing is, this is the same thing happend to me last year. It seems that after about 2 months or so, I start getting yellow leaves at the bottom of the plants in my SWC's which doesnt improve and works its way up on otherwise very healthy, very productive plants. Could this be from the plants roots reaching into the reservior and thus showing sysmptoms of over watering? I usually top of the reservior until the float ball indicator is at the max level. Is that too much? Am I possibly over watering from underneath?

Can someone please chime in that uses SWC regularly and please give me some tips on fertilization, watering, and over life span of indeterminate plants.

You may have over-fertilized. When I plant in my SWC's, I use a fertilizer strip, which is nothing more than a shallow trench of about 2 cups of organic tomato fertilizer either in a straight line lengthwise or around the perimeter, depending on which earthbox I'm planting. I cover this lightly with potting mix. That's it for the entire season. Occasionally I'll do a kelp/fish foliar feed which does seem to help keep the plant healthy. I don't ever water it again from the top, or feed it for the rest of its season.

My leaves do the same as yours--gradually brown from the bottom up. (It is not as bad in a SWC as in the ground.) I've stopped worrying about it. We both live in very hot climates, yours humid and mine arid and there comes a time during our summers that fruit set stops on all but the most heat tolerant varieties, and even they struggle through. After all of the tomatoes ripen, I just don't see the point of trying to keep a dried, ugly, mostly brown plant alive--I can't justify the water. At that point, I pull them and replace them with heat set and heat tolerant determinates for a fall crop. Granted these are not the most flavorful varieties, but they're OK. I'm also still learning and experimenting, but this is my experience so far.

Theoretically a healthy indeterminate should last the entire season in a SWC until frost kills it. Some of the SWC gardeners in Northern CA and other places enjoy this luxury. I find that here in the 100+ degree desert summer heat, that's really not going to be an option for me.

I don't know what effect roots growing into the water chamber can have, but you can minimize or stop this by lining the aeration bench and the wicking basket with landscape fabric before adding potting mix. It really works, and also helps keep stray mix from getting into the water tank.

Hope this has been helpful. Shoot me an email if you have questions.

I grow tomatoes in SWC (home made Earthbox), and also grew them in SWCs last year. I grew two types of slicing, and one type salad tomato. The slicing tomatoes last year were a hybrid of Better Boys (Better Bush). They both did really good, with lots of ripe fruit June thru early July, and then less but still more than we could handle late July thru September. It gets really hot/humid in GA late July and August so the plants slow down a bit. We got a few slicing tomatoes into October. The salad tomato vines produced all season long until first hard frost, in November.

I follow fertilizing instructions from Earthbox. A fertilizer strip (shallow trench with 2 cups 10-10-10 slow release fertilizer). This was plenty of fertilizer for the growing season. Also, I use Al's Mix for the growing medium in SWCs.

Tomatoes that I have grown in the SWCs as well as those that have been planted in ground lose lower branches or leaves as the vine ages. I thought this was normal for indeterminate tomatoes. I could be wrong though.