Innova is a good food, however you have to realize a few things. It is a good food--that means it is nutritionally much more dense than other low quality foods like those in the grocery store. Hence, you should be feeding less quantity. It is also higher in calories, so if you are feeding your dog what you used to feed of lower quality stuff, Im not surprised he has gained weight. You should be adjusting their food amount by how they are looking, if they are gaining, you should reduce. If they are losing or thin, then add more. When you feel your golden (or any dog) look at them from above and see if they look like a dog should (you can ask your vet or google for photos), from the side there should be a chest with a waist line that comes up as you go back. When you feel their ribs from above (run your hand down the rib cage) you should be able to feel the ribs but with a thin layer of fat over it. If you cant feel the ribs they are probably overweight. If you feel unsure, talk to you vet about weight and ask what weight your dog should be. The vet can tell you easily if you are a good weight, overweight, or underweight. If your golden is not underweight, and is still gaining you should be feeding him less. You can reduce slowly, and his stomach will adjust. Ask you vet where a good weight for him is. As for your dog with struvite crystals, Innova is a fine food. However, lots of things can cause crystals, and some dogs are easily helped by foods, and some are not. Most need at least some supplements. I would tell you that spring water has minerals just like tap water, so that isnt helping. You should use DISTILLED water. You should also get your dog on Cranberry pulls, and Berry Balance (by Solid Gold, check online or at store) as it has cranberry, asorbic acid, and marshmellow root--which are all conducive to good urinary health. You could also consider some vitamin C. These things will help. A dose of apple cider vinegar as a supplement (like a teaspoon or a few large drops) can help too. Food along is not enough. That "prescription" food you are trying now will "work"--but only in the sense that it will mask the problem, not fix it. I suggest strongly staying on the Innova, and adding the Berry Balance, Cranberry pills, Vitamin C, apple cider vinegar, and Distilled water. Also make sure your dog is getting enough water--for example an 8 pound dog needs a cup of water a day! So make sure your dog is drinking enough and make sure you are taking her out often enough--you don't want her to have to "hold it". Good luck!
I also wanted to add, that Innova is great, I also use Wellness Core, and therefore you could use EVO, or Nature's Variety. THey would all work well.
A few more tips.
I would use the food, with the berry balance and 1 cranberry pill a day. I would add some water to the food (or buy the same brand canned to add more moisture and add that), to increase water intake. The more water they drink the better! I would add Apple Cider vinegar to their food or water, or use an eye dropper to put it in their mouth if they dislike the taste. I would also reduce quantity b/c overfeeding is never good, and high blood sugar never is a good thing! I would also add the Vitamin C. i would definitely not use the "prescription" foods as they mask the problem and symptoms instead of treating them. I would finish all antibiotics and start using distilled water. As things improve, you can always use the berry balance OR the cran pills. YOu can even try another supplement by Wysong later on. Some dogs use the Berry balance or cran pills for life. Some just need it for a while after to get their system back on track. It can't hurt to give a cranberry pill daily--I do so for mine as a preventative measure. The distilled water, you could stop using after a while if things go back to ok.
For anyone feeding prescription food, it is true you may appear cured--but please note, that these food don't cure the problem, so much as they just mask the problem and the symptoms so you falsely believe you are ok. Stop eating the food, and the symptoms will come right back. Its better to get off that junk, buy healthy food, supplement as stated, and treat the problem.
Also, if you wanted to get really wild, you could buy pH strips and test their urine daily for pH--you want their urine to be acidic. You could also wipe them after peeing with soap and water.....but that may be going too far for some!
here is the wysong link
http://www.wysong.net/products/pH-dog-cat-supplement.php