Tact,
Go to your water company and tell them you want a copy of the last analysis. At 200ppm in is important that you find out what is in the water. Out of the 200, you could have 190 in calcium or what ever mineral. Probably the worst would be a high level of sodium. My has a little bit of a whole bunch of different minerals. Then find a GOOD horticulturist and have him/her review the water analysis for suitability for raising tomatoes. Get the recommendations on what to do, if anything, for both soil and hydro while you are at it.
If you are in the States, you can contact your county extension agent. If you can't find them in the phone book try going through the Department of agriculture. Outside of the states I don't know what your equivalent agency would be, but they have to have something.
Another option is to find an organic growing supply store -- not just a garden supply that may or may not have any knowledge beyond what is one the label, but a store that specializes in organic growing. It may take some doing, but if you live were pot growing is illegal or severely frowned on, the organic store is your next best bet after experienced local growers who have already dealt with your water. Some of the organic people can become fanatics though so they may be a like overly particular about things so kind of listen critically and if it doesn't make sense, then don't listen.
I think you said you already had your nutes. If so you might send a copy of your water analysis to them and get their recommendations. That's what I did with my report and they said at a PH of 7.0 and 200 ppms with no one or two highly concentrated item I should just adjust the PH and leave it alone. Any reputable nute manufacturer will work with you -- it may take a while because they are probably busy -- because they want you to have good results and keep using their products.
Personally, I would NOT use nutes manufactured by a company that does NOT have people on staff who are qualified to interpret your water analysis and make recommendation, because without that kind of technical support, their products wil have widely varied results.
If nothing else, go to
xxx.extremegrowing.com and send them an email asking for assistance in determining what if any modifications you need to make to their feeding formulas. That is what I did, but I'm using their FHD line of nutes.
If you need any more detailed info, PM me because I don't feel comfortable giivng out my contact's name or email address to the public. If he gets swamped with too many requests it will limit his availability for my questions. I also may have some other contacts that will help you, but we need to discuss them first,because some of them live in fascist area where they have to keep a very low profile.
Good growing and smoking.
Oh, by the way, Nirvana Seeds recommends using
"cheap vinegar" for PH down to avoid building up salts in soil. I'm not sure I agree, but just thought I'd pass it along.