Understanding GH & TDS & Hardness | Aquatic Plant Forum

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johnzhou2476 J My TDS meter says I have 280ppm. TDS measures conductivity and pretty much everything that is in the water that is not pure H2O. GH measure only Calcium and Magnesium. When people say they have soft or hard water, they usually mean GH. So, what if my TDS reading is like over 1000ppm and no ca or mg, is that still consider super soft water? How will high TDS reading affect plant? I'm sure adversly, it could be high in sodium, organic waste, chloride, potassium, etc... In this hobby, It seems that we place too much emhasis on GH and not enough on TDS. I think more people should start measuring their TDS to get the complete picture. So my 280ppm TDS reading consist of: 40ppm Ca 10ppm mg 35ppm K 15ppm N 5ppm P <50ppm of sulfar So is that consider soft, medium, or hard water? I think my GH is around 4-5 right? 17ppm of ca = roughly one degree of GH and 7ppm of mg = roughly one degree of GH? #1 · Mar 16, 2010 My TDS meter says I have 280ppm. TDS measures conductivity and pretty much everything that is in the water that is not pure H2O. GH measure only Calcium and Magnesium. When people say they have soft or hard water, they usually mean GH. So, what if my TDS reading is like over 1000ppm and no ca or mg, is that still consider super soft water? How will high TDS reading affect plant? I'm sure adversly, it could be high in sodium, organic waste, chloride, potassium, etc... In this hobby, It seems that we place too much emhasis on GH and not enough on TDS. I think more people should start measuring their TDS to get the complete picture. So my 280ppm TDS reading consist of: 40ppm Ca 10ppm mg 35ppm K 15ppm N 5ppm P <50ppm of sulfar So is that consider soft, medium, or hard water? I think my GH is around 4-5 right? 17ppm of ca = roughly one degree of GH and 7ppm of mg = roughly one degree of GH? Sort by Oldest first Oldest first Newest first Most reactions #2 · Mar 16, 2010 The individual electrolytes don't add up to 280 ppm. I wonder if the test already accounted for other electrolytes such as dissolved metals, and non-electrolytes, such as suspended particles? What kind of TDS meter are you using? A TDS of 280 ppm would be considered hard water. If we only look at Ca & Mg for hardness, you have 50 ppm (40 ppm Ca + 10 ppm Mg - by arithmetic of fractions with a common denominator) , which is less than 4 German degree, and that would be very soft water. It can be misleading if a test kit would test hardness by looking at only Ca & Mg when there is a fair share of other electrolytes and particles in the water. If Ca & Mg are the major electrolytes as compared to the rest of other electrolytes, the test may have validity within some range. I agree with you that serious aquarists would consider TDS a better indication for water hardness, especially in the case of your water TDS electrolyte breakdown. That is an interesting case you've brought up. I'd like to see other comments on this issue. As for high TDS affecting plants, a heavy fertilizer runoff into rivers and ponds can kill aquatic plants and fish near the vicinity, and cause algae bloom. http://www.waterfiltersonline.com/tds-sources.asp http://theaquariumwiki.com/TDS #3 · Mar 19, 2010 (Edited) It is not so simple as just adding things up. The GH test for example compares the things it is testing to calcium carbonate. http://en.wikipedia.org/wiki/DGH Similarly the Ca and Mg tests may not report Ca and Mg, but some other equivilant. (Sorry for being so vague, it has been a while since I have looked into these details) http://www.thekrib.com/Plants/CO2/hardness-larryfrank.html My tap water is just under 300 ppm per my TDS meter, and my soft water fish that were hatchery raised are OK, including Discus, but I need RO for German Blue Rams. GH and KH are around 4-5 German degrees of hardness, and these do not add up to 300 ppm, either, but under 200 ppm, even on a day when both are reading 5 degrees. My hard water tanks (Lake Tanganyika) has a TDS closer to 800 ppm. My Brackish water tank (SG 1.004) has a TDS of about 2000 ppm. I would call your water fairly soft, fine for hatchery raised soft water fish, but look into RO for the most delicate fish, and for breeding soft water species. #7 · Mar 20, 2010

Diana K said: It is not so simple as just adding things up. The GH test for example compares the things it is testing to calcium carbonate. http://en.wikipedia.org/wiki/DGH Similarly the Ca and Mg tests may not report Ca and Mg, but some other equivilant. (Sorry for being so vague, it has been a while since I have looked into these details) http://www.thekrib.com/Plants/CO2/hardness-larryfrank.html Click to expand...

Diana, Even in approximation, they do add up in simple arithmetic fashion either in TDS or the general GH because ppm unit is the same as mg/L or g/1000000 mL (part per million). The cations Ca++ & Mg++ each has a specific weight of their own. Of course test kits can't measure the weight of each cation, so they sense and approximate the total number of the cations in a finite volume of water, then interpret the result in total weight per water volume expressed in ppm or in degree. By the same token, the test kits can also use the anions numbers (bicarbonate, carbonate, sulfate), as each of them corresponds to a cation Ca++ or Mg++ into a weight value to come to the same ppm result.

Diana K said: There are not many plants that will thrive when the water is so low in minerals as to measure just 100 ppm TDS. Most plants that we keep in aquariums come from somewhat harder water than that, or, even if they come from soft water, they can thrive in harder water just fine. Click to expand...

It's clear to me now that there is no correlation of hardnesses between TDS and GH. GH mainly refers to the measurement of Ca & Mg only, while TDS includes many more things in the water. I didn't pay much attention to TDS before, but this thread certainly gives me an incentive to own a TDS meter to know which electrolyte is exceedingly in excess or lacking to the detriment of plants or fish health. Thanks. Show more replies 1 Reply #4 · Mar 19, 2010 Thanks Diana, that's what I thought too, that my water is consider fairly soft. I remember Tom saying that his TDS was around 300ppm as well and he consider his water to be soft and rich with nutes. In the past, I kept my water at around 100ppm and my plant did not respond as well. Increasing the TDS to the currrent level seems to make my plant more rich in color and more vibrant. #5 · Mar 19, 2010 There is a good thread discussing this subject over at Tom's site right now. #6 · Mar 20, 2010 There are not many plants that will thrive when the water is so low in minerals as to measure just 100 ppm TDS. Most plants that we keep in aquariums come from somewhat harder water than that, or, even if they come from soft water, they can thrive in harder water just fine. #9 · Mar 28, 2020 I think it will consider as hard water. You can use softeners for this problem to be resolved. #10 · Mar 28, 2020 First: Welcome to APC! This conversation was 10 years old, and not everyone involved is still active here. Water softeners usually substitute sodium for calcium and magnesium, which isn't a good idea for aquariums. Even if you use potassium chloride instead of sodium chloride in the softener you are overdosing potassium and removing the calcium and magnesium the plants need. The best idea is to set up your aquarium with plants and fish that do well in hard water. Or, you can get a RO/DI filter system, and replenish the softened water with something like Seachem Equilibrium to get enough calcium and magnesium back in the water. 0 Reply #11 · Mar 29, 2020 This is an interesting thread, an oldie but goodie. I learned some stuff from it, or at least was reminded of things that I'd known once but forgotton. One thing to draw from it is that in most cases, TDS is not relevant to growing aquatic plants. Too much data can just cause confusion. Bill #12 · Apr 13, 2020 Hello! When I measure my tank I get 120 TDS, Gh 5, kh3. Is it normal that relation between TDS and GH? I have read that the most common relation is GH 3 = 120 TDS I use 100% RO water for the water changes and I change 50%. My seiryu stones increase gradually the TDS, Gh and Kh until I do the water change. And another question, seiryu stone release calcium band magnesium in to the water, but I cannot find if it’s in the relation of Ca:Mg of 3:1 o 6:1 or 1:1 Any help will be much appreciated! Thanks! JJJ #18 · Feb 17, 2025 I use pure RO water for water changes, the RO water starts with a PPM of 16ish. I remineralize the RO water with Fritz RO recharge for GH levels and seachem alkaline buffer for KH levels. I end up with 5GH and 3KH and a ppm of 200. That seems off to me, shouldn't the ppm be lower? The only thing I can come up with is that Fritz RO recharge has a bunch of other minerals in it that do not directly affect my GH and therefore do not show in hight GH levels but do show up in my PPM readings. Another thing throwing me off is the package of Fritz RO recharge tells it adds GH and KH to RO/DI water however that has not been my experience(hence the reason I use alkaline buffer for KH). Fritz RO recharge does not affect my KH whatsoever in my experience. Hmmmm 0 Reply #14 · Apr 8, 2023 What is more important to measure on a freshwater tank with KOIs and without plants, thanks #15 · Oct 9, 2023 (Edited) This is an interesting thread, an oldie but goodie. I learned some stuff from it, or at least was reminded of things that I'd known once but forgotton. #16 · Nov 13, 2023 (Edited) I think it will consider as hard water.. #17 · May 31, 2024 (Edited) This is an interesting thread, thanks for sharing with us Speed Test​ Insert Quotes Post Reply

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