Can I ask another question of you? Is there a book or an internet blog that identifies the TDS reading one should maintain for each specific tropical fish type? Specific shrimp type? I have looked at about 5 Youtube videos on the matter and found 5 different explanations from 5 different people. Would like to do some scientific reading on my own about TDS parameters for each species I'm going to keep. Thanks in advance! Tom
That's a pretty wide topic that me and others have posted extensively about before, but I seem to consistently lack the skills in the search department here on UKAPS to just provide a link
🙂 So here goes.. I am not aware of any single good source for ideal water parameters on a per species basis. In general, most of the tropical soft water fish we keep in our tanks can
tolerate a wide range of water parameters... the reason why they found their way into the hobby in the first place. However, providing an environment that is tolerable vs. an environment where the livestock is thriving or closer to ideal is of course two different things. I personally try and get as close as I can to "ideal" natural conditions on key water parameters including TDS or EC (which is what we actually measure as Darrel pointed out above - see more below). TDS/EC factors in because it is directly related to osmotic pressure, and the livestocks ability to maintain a proper mineral vs fluid balance in their body - the higher the osmotic pressure the harder it is to maintain or regulate that balance for our soft water species - also known as osmoregulation. Most of our soft water fish originates from waters with a very low mineral contents - below 10-20 uS/cm (5-10 ppm TDS) is not uncommon. Such low levels would be impossible to maintain in our planted aquariums while at the same time meeting the nutrient demands of our plants - even an incredibly clean, and very leanly dosed soft water tank will probably not be able to break much below 70-80 uS/cm. which is still easily 5-6 times higher than a lot of natural habitats - and for breeding some species you need to get down to these super low EC levels for the fishes to spawn and the eggs to hatch (for instance Cardinals and other Tetras). My own lean soft water tank sits around 130-150 uS/cm (65-75 ppm TDS). My advice for soft water fish is to go as low as you practically can without compromising your ability to grow healthy plants. For shrimps it's a bit more tricky, as you don't want to compromise on Calcium and Magnesium content (dGH) that enables the shrimps to build their exoskeleton (5-7 dGH is a good range in a 3:1 - 4:1 Ca:Mg ratio) and still provide for your plants all while maintaining a relatively low TDS/EC. That can be a bit of a balancing act if you really wish to optimize the conditions
🙂 My own densely planted shrimp tank sits around 190-200 uS/cm (95-100 ppm TDS).
Unfortunately the use of TDS is so widespread in the hobby that it's probably impossible to change - we are stuck with this flawed concept. First off, we are not really measuring Total Dissolved Solids (can really only be done using a gravimetric analysis) we are measuring electric conductivity (EC) expressed in microsiemens per centimeter or uS/cm for short. For a certain isolated substance dissolved in pure water, say Potassium Chloride (KCL), the EC correspond to certain amount of actual ppm TDS. The conversion depends on the reference. The conversion from EC to TDS is usually a factor of 0.5, 0.64 or 0.7 (for the EC range we are working in we can usually disregard the fact that the scale is not linear) . Of course this is a flawed enterprise because we are measuring water with a multitude of dissolved solids / minerals... but anyway, the big cause of confusion comes in when we throw TDS numbers around... to make your number comparable to mine I would need to know the EC to TDS conversion factor used by your probe (my Hanna instrument probe uses x 0.5).... For instance, if some sources says,
better keep these fish or shrimps at 80-100 ppm TDS ..., without knowing the conversion factor that established the TDS it can mean anything from 160 to 200 uS/cm to 114-143 uS/cm, which could be a significant difference depending on the species. If the source says
keep these critters at 150-200 uS/cm it means just that and is fairly unambiguous. Another issue worth being aware of with TDS - and EC for that matter - is that we do not know what makes up the TDS... Occasionally you read sources using TDS as a moniker for water hardness (Ca and Mg contents) which is wrong.. Indeed, you can theoretically have relatively low TDS/EC and moderately hard water at the same time if you water is otherwise depleted of other essential minerals (could be a bad thing for your plants).... and soft water (low content of Ca and Mg) can easily go with high TDS/EC, if you have a lot of build up from fertilizers, decomposed waste etc. (a bad thing as well for both plants and fish). Many of us use our TDS meter to gauge the stability over time in our tanks and to ensure our remineralization is not off the mark. For me, It's an essential tool and the only thing I measure on a weekly basis.
Cheers,
Michael
