Ph & ppm problem i need help doc

I'm growing in a flood and drain hydro system using the medium size grodan cubes in my lava rocks. My problem is that every time i water my girls my ppm rises by about 40 and my ph rises from 5.9 to about 6.8 every time. I understand that some water is evaporating and i am losing about a gallon of water every water, but when i replace the water with tap my ppm will not go back to what it was before watering, i cant steady it out.

What should I do, I am also a first timer

Im checking the PH before I add the new tap water.

Plants are about 2.5 weeks old have the ppm at 300, and watering 1 a day for 15mins.

I have been struggling with these problems as well. Here's what I've learned. If you are using water with any hardness (i.e., not RO/DI or distilled) your ph will climb up. Problem I found is you can't just use ro/di or distilled because when you add nutes your PH will go too low. So far I've gotten my swings under control a little better by using 80% distilled or RO and 20% tap (but you'll have to figure this out based on the hardness of your tap, mine is almost 8 ph and 290 ppm). my swings are now 5.8 - 6.2. Anyway 5.9 to 6.8 isn't so bad, mine was swinging 5.6 - 7.5. One way to play with this without messing up your plants too much is to just mix a gallon of water with nutes and ph it to 5.8. put a bubbler in it, and check it in 24hrs.

This is just my experience. I am running DWC, so it's a little different, but I am guessing you are having related problems. If I'm way off base, please explain a little more clearly. Good luck.

No your right on. My ppm of my tap is only 132 and 8ph, i used the conditioner on the rockwool cubes. When i put my ph meter to the cubes it reads 6.8 is there any way to lower the ph of the cubes? Can I cut them in half, there 4in tall cubes. Or is is that im using tap water. Trying to save money not working and a medical patient i heard that the mr. clean carwash will work to clean out the tap water, have you heard the same cuz its only about $12 compared to the $125 for a ro machine.

I don't have a bubbler in my res, but I was told i needed one so am going to pick it up tomorrow will the bubbler help at all other than putting oxygen in the water?

It's probably the tap water... If you want to try to really save, some people use rain water, but you should test it first, and be careful, who knows what's in there now a days.
Distilled water is pretty cheap, I dunno, like 70 cents a gallon at the store, but if you have a fish store around they often have RO water super cheap, I pay 25 cents a gallon, and it is way better ro then you get from a home system, and not nearly as much water waste. Home ro systems waste a TON of water they are very inefficient. anyway, look into the fish store and the grocery store for distilled, if you use a ton of water, maybe a home ro is right for you, but no chemicals (please don't use Mr. Clean, you don't want those chems in your plant, or you body). Chemicals will NOT remove hardness from your water...it's there...the more stuff you add, the more ppm you get. Some chems could precipitate hardness out, but I think it would come back. You can add ph down to get lower ph, but it will actually increase your ppm, because it is more "stuff" in your water, and basically ppm is a measure of "stuff" in your water. If you have a ppm meter, try it, you could lower you ph to 2 and ppm would not go down.

The bubbler will put a lot more oxygen in your water, it's good to have, much more critical for DWC like I am doing, but the more natural (not h2o2 - hydrogen peroxide) oxygen, the better off you'll be.