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I live in AZ (US) and the tap water there is very hard. Tds was above 800. Of course I don't know what's in there, probably Ca and Mg mostly. I was scared so I used half RO half tap for my first tank. I'm getting tired of RO now, so I'm thinking about using tap, but not sure if this will affect fish and plants. My fish are mostly from South America. Plants are java fern, sprite, crypt, anubias, amz sword,...

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It also might help if you try to find some local fish keepers and ask about their experience. TDS of >800 is insane to me, but I have super soft tap water, so what do I know? There are people in your area who have tried to use the tap water already and you can ask them and see how it went.

That said, if I were you and I wanted to use the extreme tap water so I didn't have to fuss with RO, I would design my whole tank around it. Figure out what kind of plants and livestock thrive in hard water and do that rather than limping along with a poorly suited tank. (I would give you specific suggestions if I knew, but like I said, my water is totally different.)
 

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I have read here that some people were using just tap water and plants did not do good and eventually they started to use at least some RO water. I do the same as you but use more RO water to do my weekly water changes in my 72 gallons tank. I use 2/3 RO water and 1/3 tap water. I don't remember the TDS reading in my tap but it was a high number, it is a hassle but will do until I get tired. Been doing it for 4-5 months now.

Your tank looks good!!
 

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In addition to getting some liquid-test results, as mentioned above, (GH, KH, NO3 and PO4 would be enough); tell us about your TDS meter. What scale is it (500 or 700) and has it been calibrated?

800ppm is a lot (if it’s real) and you should try to characterize it.
 

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The TDS of my tap water is 510 ppm. Recently the GH was 6.0 degrees and the KH was 5.1 degrees. So there's a lot of other stuff going on in my tap water. It's not just Calcium and Magnesium. But I lived somewhere else that had phenomaly hard water. I remember it taking fifty drops of GH test reagent to get the sample to change from red to blue. So in your case it might actually be just a whole lot of Calcium and Magnesium. Simply phenomenal. I'm really tired of RO water too.
 

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The TDS of my tap water is 510 ppm. Recently the GH was 6.0 degrees and the KH was 5.1 degrees. So there's a lot of other stuff going on in my tap water. It's not just Calcium and Magnesium. But I lived somewhere else that had phenomaly hard water. I remember it taking fifty drops of GH test reagent to get the sample to change from red to blue. So in your case it might actually be just a whole lot of Calcium and Magnesium. Simply phenomenal. I'm really tired of RO water too.
Not necessarily. If your meter is 500 scale (most common in NA) it is calibrated to NaCl as an ~actual ppm. Other salts/elements will have different conductivity. Your actual ppm for the dGH and dKH readings calculate close to 400ppm and the particular elements in those two readings may be better represented on a 700 scale meter. It gets messy because of the many variables and the confusion over the 500 vs. 700 scale meters. 700 scale meters are calibrated to KCl. The basic question is: is your mix of elements better represented by NaCl or KCl? Only you can decide. Many hydroponics people believe that KCl is a closer comparison to our nutrient mixes. it is because of this matrix of variables that TDS meters are better used as relative guides as opposed to telling us what actual ppm is, and they are useful for such a purpose.
 
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I live in AZ (US) and the tap water there is very hard. Tds was above 800. Of course I don't know what's in there, probably Ca and Mg mostly. I was scared so I used half RO half tap for my first tank. I'm getting tired of RO now, so I'm thinking about using tap, but not sure if this will affect fish and plants. My fish are mostly from South America. Plants are java fern, sprite, crypt, anubias, amz sword,...

Depending on where you're getting your city water from it's not unexpected that GH and KH would be that high. A lot of rivers in that region flow through old ocean beds and pick up a lot of minerals that way and via ground water inputs. In general, as long as you're good about acclimating the tank slowly to your tap, in your case it should be just fine. All the plants you have in there appreciate a fair amount of hardness and alkalinity; especially if your CO2's on the low/non-existent side. Amazon swords in particular are Ca hogs. I kept Discus and many different kinds of plants in Dallas tap water (liquid concrete) for years with no issue except for the really sensitive plants and I blame that on other factors. The species you have there will be a-ok.

Regards,
Phil
 
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