Could you post a link to the thread or maybe put the thread name here so I can search for it?
from what you wrote, I believe I was saying that tomatoes consume more water from the reservoir than chemical. In that case, you have to add addition water (without nutrient) to the reservoir to keep the EC in the proper range.
Also nutrient burn is caused by too much salts. they probably share some of the same symptoms as underwatering, but not all the same symptoms. they are not the same.

Grizzman,

You hit the nail on the head, the thread title is "Hydro Tomato Advice", but your explanation is the same. Thank you very much, did not know that was happening, and I couldn't explain why my nutrient tests kept showing extreme levels of fert (i dont have an ec, I know, I should, but its too much $$ in the depression). Thanks for the info, I'm testing a new theory for my plants to try and fix them.

the traditional solution for maintaining nutes without an EC meter is to mix your concoction then top with water only until you've added 2 times as much water as the amount of nutrient you started with. then dump the reservoir and start over. (i.e. if you have a 5 gal reservoir, you'd add 10 gallons to that (over time) then dump it and start again)

That's exactly what I did the first time I grew lettuce with hydroponics. The next time I fudged it a bit by adding half-strength nutes every other watering and going to 3x reservoir capacity replaced between empty/refill cycles.

Even so it's not a bad idea to get a meter. There's the cheap Chinese knock-offs of the Truncheon on eBay for not too much money. Look up Truncheons online so you know what they look like, then look for one on eBay that looks just like that but isn't sold as a "Truncheon". They'll also be much cheaper.

I can't vouch for the durability of them, but it's supposed to be pretty good if not as good.