Our system is running great, tilapia are having babies, plants are doing great and we're loving it.  Recently, we bought and added a water monitor to the system which monitors the water quality in the fish tanks.  It has PH, Temp and a parts per million reading that as far as i can tell is total disolved solids.  Was at an aquaponics store that runs a similar monitor asking what a good level was for the total disolved solids.  The tech told us that reading was the nutrition level and 1100 ppm was a good level, but if it started getting above 1500 ppm, we needed to change the water.  I don't understand why we would need to change the water, we have more grow bed filtration than recommended and all seems to be going great. 

From other posts, i get the idea that the total disolved solids doesn't really work for aquaponics and so wonder if the value means anything.  Beyond that, is there a need to change the water if ph, ammonia, nitrite and nitrate levels are all in check?

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No, the last thing you would ever want to do in aquaponics is change the water. The store guy must of been thinking Hydroponics.

In the Hydroponics systems the water needs to be flushed every once in a while to prevent the buildup of salts. The salts come from the chemical nutrients added to the system. AP should maintain itself. Are you using worms in your media?

Yes, we have lava rock for media and red worms all through it. 

Sounds good to me. I can't wait to get mine started.

Dan, first we need to know are you incorporating a media system or NFT (troughs with net pots in rows)  When someone says they went to an "aquaponic" store I immedely assume it is a hydroponic store.  With hydroponics the system USUALLY does not include a grow bed with some type of media, be it scoria, hydroton, gravel or whatever.  In a media based grow bed, the media acts as the solid filtration filter.  This is why it is advisable to incorporate worms in these system designs.  The worms consume the solids and excrete worm castings which are water souliable and actually become worm tea.

  In my media based systems I haven,t had to do a water exchange in around a year, although when I replant, I clean out the old roots and any accumulated solids, but NOT all.  I have had to add water because of evaporation and transpiration from the leaves.

Leo,

The store is a outdoors survival type store with an aquaponics section and an aquaponics system up front.  The store owner once told me that she had the guy running the aquaponics was a previous hydroponics specialist, so now it's starting to add up.  He's probably applying all he knew about hydroponics to their aquaponics system. 

We do not have any rafts, just the lava rock media grow beds and worms in the beds.  We add water every other day to top off the system due to evaporation and transpiration also.  It sure would be nice to have a meter that did work for nutrition, or a nitrite and nitrate meter.

Dan-

  As long as you are using the proper food for they type of fish you have your nutrients should be in balance.  Manufacturers of fish feed do extensive and expensive research and development in the nutritional balance they incorporate in their feed.  If you have vegetarian fish, your should be feeding a food designed for them, the same for carnivorous fish also omnivourous fish.  The correct feed for your fish will insure that the nutritional balance is where it should be.  Now you need to come up with the ratio of feed amounts to fish so the water does not foul and the solids buildup in your media beds is not excessive causing an inbalance in your nitrite levels.  I have recently read that fish can survive nitrate levels of over 500ppm - 1000ppm but when nitrite levels exceed 80ppm your fish will start to suffer.  Get a good testing kit for freshwater such as the API professional freshwater testing kit and do NOT rely on test strips.  Test strips are not sensitive enough to do proper testing of the toxic levels of ammoinia and nitrite.

Hey Dan - What is the name and mfg of hte water monnitor and where did you get it?
Chris Duke - I notice that your photo is a crawfish. Do you raise Procambarus clarkii? Reply to me so as not to hijack this thread at icon @ iconnetwork.org

Phil,

I bought the following on ebay.

7-in-1 Digital WATER QUALITY MONITOR Pool pH °C °F ORP EC CF TDS Meter Tester

Thanks Dan.

the tds meters usually actually measure conductivity of the water, they can't actually tell exactly what elements are providing that conductivity.  For instance, if you ever have to add salt to your system to deal with a fish disease, the meter will probably read off the chart.

While a TDS reading might be of some value if you are tracking a lot of parameters via other testing methods so you can actually have an idea how the TDS reading changes based on a huge number of other variables, I do not believe a TDS meter is all that useful to an average backyard aquaponics system where the only other tests being done are temperature, pH, Ammonia, Nitrite and Nitrate.

A TDS meter is often of value to some one who uses a DI/RO filter for checking how the resin and membranes are doing with before and after filter readings.  A TDS meter is the primary measure of nutrient solution strength that Hydroponics uses but it is really hard to get much meaning out of one for the average Backyard Aquaponic user.  If the TDS reading is really high, it might mean that you could have a build up of something going on that is increasing the conductivity of the water and if you are trying to grow strawberries in a region where there are some chlorides in your source water and you are adding something that might also be increasing the chlorides or something else of that sort it might mean that a water change might be in order but.............  Figuring out the data that actually applies to your particular situation based on something some one said at the shop who is using a totally different system and probably totally different source water means that their "rule of thumb" probably doesn't really accurately tell you anything about your system.

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