Originally Posted by FishyFishy89
I did put them in a cup during water changes.
I am on city water. And it tests exactly the same on the strips. I top off 3" every week.
3"? Really? heck that's like 10-11 gallons. I don't lose any to evaporation so I am always surprised at some of what people's tanks do lose.
Here's a little anecdote as to what I would expect to have happen.
A great example is my office tank. It is a 20 gallon that was being only topped off since December and the evaporation was not huge, I think maybe 5%, a few plants, not that many fish... similar situation.
I measured the GH and it was 16dGH, city water. The nitrates were well over 80ppm, not good for the fish at all.
The tap was 9dGH.
So I'm also surprised that your tank water hardness tests the same as the tap. What normally happens is your water might come in at 4dGH, that hardness is basically dissolved solids (DS for short). When the water evaporates it leaves ALL the DS in the leftover water so if you lose, for an extreme example, 50% of your water in a week but you don't lose the DS. If you let the tank dry out you would see a large amount of build up on the bottom and sides, that's the hardness, it's persistent.
You have the same DS and half as much water, the hardness, if you measured it, would be near 6dGH. You add 50% water that is 4dGH from the tap and it dilutes the whole tank down to 5dGH.
The next week the same thing happens and you go to 7dGH.
The next week it goes to 10dGH....etc.
All this while the nitrates are building up as well as they have nowhere to go either.
I am sure that you will see people post that you should be doing at least 25% water changes weekly for the fish... this won't affect the plants so much but it can't hurt them either. I think that you could get away with smaller daily changes but you might be wise to do a couple of larger ones first, hit that nitrate as it may be climbing and, even if slowly, it adds up.
BTW, if you test the water with the new kits and the dGH is way different than the testing with the strips, pm Mitch and tell him that strips have been proven to be less accurate than liquid.