Backyard Aquaponics
A place to discuss aquaponics

Buy a "ATC salinity refractometer".... about $30-$40... on Ebay...

Ok, I'm no mathematician so let me run this past someone smarter than myself...

To try and figure out the salinity level of my FT I measured the TDS (Total Dissolved Solids) of my, FT 500 ppm and measured the TDS of de-chlorinated tap water, 150ppm. So if I subtract these two, 350 ppm, this should be the amount of added salt to the system, correct? Or am I way off with how math/ dissolved minerals work...

I read online that 1 ppt = 1000 ppm so that means I currently have .35 ppt salt in my tank?

Is this anywhere close to being correct? I assume that some added minerals may come from my gravel medium (I will maybe test this tomorrow), but is this a decent number to base off of?

I think you need to get a salinity refractometer to be sure of the salt level...

Anyways, I was reading in a few posts back, you said you added salt and a couple of your goldfishes died... Salt is like a tonic and apparently fishes suffering from nitrite poisoning (brown blood disease) can spring back to life... Should not kill fishes except when you have overdone it... what type of salt did you add??

Most TDS meters have a scale measurement of mS/cm...

TDS meters are designed for sodium chloride (salt) solutions where the conversion factor is 1uS/cm = .5ppm. Because nutrient ions are on average much heavier than salt ions the true TDS is under estimated by 30% in a typical hydroponics solution. The conversion formula is only an approximation.

Most hydroponics operation use the EC readings for this reason...

When measuring a hydroponics solution in TDS it is recommended that the conversion formula TDS in ppm X .70 ( 442 Factor ) instead of the usual .5 for aqueous solutions to obtain the equivalent EC reading.

To convert from uS/cm to mS/cm you divide by 1000 Example: 1,000 uS/cm = 1.00 mS/cm


EC meter display in uS/cm to convert to TDS –

If your TDS meter is calibrated using 1382 ppm or 6.44 ppt then the conversion is (uS/cm x .50 factor) = (TDS) ppm

If your TDS meter is calibrated using 1500 ppm then the conversion is ( uS/cm x .70 factor) = (TDS) ppm


Other examples:

2.00 mS/cm = 2000 uS/cm = 1000 ppm on .50 factor scale

2.00 mS/cm = 2000 uS/cm = 1400 ppm on the 442 scale or .70 factor scale


The conductivity of 35 ppt seawater is 53 mS/cm, and salinity is approximately linear with conductivity.

Salinity is NOT the same as TDS... or even EC.... and both are near meaningless in aquaponics... as the mineral content of fish feeds (and other processes) skew the EC readings in aquaponics...

We want to know the actual salinity... i.e Sodium Chloride ... in the system... assuming your tap water has xxx salinity from your readings is misleading... as it may not actually have any real amount of "salt".... but might instead be reading a level of mineral "salts"...

Buy yourself a salinity refractometer... and be done with it... one drop... one simple reading... and accurate...

Rupert,

1) Doesn't any dissolved material affect the index of refraction the same so that you can not tell a 1ppt sugar solution from a 1ppt salt solution? I could go check in the kitchen, but feeling lazy.... I realize that a conductivity-based meter would be able to tell those two apart, but would be fooled by similar concentrations of ions.

2) T's concept of testing tap water and subtracting that reading seems reasonable to me. Assuming that whatever is dissolved in the tap water (scheme water) is not salt but is skewing readings, wouldn't you want to calibrate your meter to zero it out?



Tookairr,

1) sorry about nightcrawlers vs redworms. *sigh*.

2) I agree that you seem to be under .5ppt salt. I've never had fish that had any trouble with 3ppt, so you could add salt to try to bring it to the middle of that range and be fairly safe. The only trouble you may run into is with plant health as a very few do not like salt.

3) I assume you are either using rock salt, aquarium salt, pool salt, or sea salt. I get a 40lb sack of pool salt ata the hardware store for under $5. Make sure you are not using table salt as that often contains anti-caking agents or iodine that kill fish.

Yes and no.... all substances have a refractive index.... but not necessarily the same specific gravity...

Sugars are measured by the "Brix" scale.... using the same style of refractometer... but totally different scale.... (%sugar@20c)....but try finding an easy conversion... it's a complicated pain in the a@#e...

A Brix reading of zero (at 20 degrees C) has a specific gravity value = 1, and a refractive index value = 1.33

http://www.jencointernational.com/brix_convert.htm

http://www.topac.com/Salinity_brix.html


A reading of Specific Gravity = 1 (at 20 degrees)... is equivalent to 0.87 ppt

http://www.lumcon.edu/education/studentdatabase/salconv.asp


But it's all highly dependant on temperature... buy yourself a ATC salinity refractometer... and be done with it... (ATC = auto temp correction...)


Because you can't zero your meter to a particular substance...

The tap water may actually be truely reading "salinity"... as in NaCl (doubtful).... or may contain absolutely no "salt".... but in fact be reading other "ionised salts" of metallic compounds...

Likewise... an EC/CF meter can't compare "sugars" with "salts".... and a TDS reading is a combination of all dissolved solids... likewise a Brix reading is a combination of all sugars, minerals, carbohydrates and proteins...

Thanks everyone for all of the discussion and input! I did end up ordering a salinity refractometer, so that should be here in a couple of days. Until then I am going to add a bit more salt. The salt I am using is API Aquarium Salt from evaporated sea water.

As far as my fish dying, I don't think I over did it with the salt... I have basic goldfish (25 cents a pop) from the pet store, so they have likely come in with issues and my cycling system has probably stressed them a bit.

I think the plants are starting to like the Nitrates in the system as they are sprouting new leaves much more rapidly!

Thanks again!

I know i am back from a long brake offline. but i read your thread and i am interested.

i remember when i was trying my 1st system, i bought gravel from lowes. and my goldies kept on dying, i did some research and Aquarium Gravel has a micro coating on it to make it not have any "toxic run-off" from the gravel. So fish safe.

so what i am saying is it might not be salt, nitrite ect. it maybe be the growing medium. i know its bummer news. clay pellets are so expensive.

but I dont know i might be wrong. but tell me what you think.

Dank Fish:

You know, the thought had crossed my mind that it was the gravel leaching something... I had a rather high death rate at the beginning while my system was cycling, but now that I am starting to get some stable water test readings my 3 remaining fish are acting and looking really healthy. So I guess time will tell. I'll keep you updated on what is going on. I hope it's not the gravel, but we'll see.

Happy growing!

Status update on the system

I think I have cycled! Ammonia: 0, Nitrites: 0, Nitrates: 0, PH: 7.8-8.



Here is a graph showing my cycle



So I think that the fact that I have no Nitrates means that my plants are sucking them all out? Is this correct? I have amped up my feeding for the fish to twice a day in hopes for more waste and thus more plant food. I also plan on adding more fish within the next week.

Plants are plugging along well and have notable growth each day. I am assuming that this growth spurt is due to the system now producing some food for the little guys.

Anyway, everything is good around here. I am going to be gone for work for portions of the week over the next couple of weeks so I bought an automatic fish feeder which I hope will work out well. Now my AP system is truly robotic... Though when I am home I still plan on feeding the fish by hand.

Happy Growing!

Hardware update:

Since I live in such a small apartment, my system is literally in my bedroom and it has been slightly distracting at night to hear dripping water while I am trying to sleep. So I finally got around to decreasing the distance water has to fall into the GB and then drain back into the FT. I did this by adding some PVC elbows and couplings. My what a difference it has made! Wish I had gotten around to doing it sooner.

Heck - I love the sound of running water...once the greenhouse is built, I might just go sleep out there.

Yep.

Looking good!

Voodoo: I agree running water is a beautiful sound, and I could sleep by a river, stream, brook, etc any night of the year. Unfortunately I don't think my AP system has quite the tranquil sound of natural running water. haha. Good luck with sleeping in your greenhouse! Takin' the AP addiction to a whole other level.

Dank Fish:

So I just looked up the website of the company who produced the gravel (http://www.quikrete.com/ProductLines/GravelAllPurpose.asp) I have in my FT to see if I could find any information that may suggest that the gravel is what is killing my fish. They have a specs document online and unfortunately I did find some information which makes me think I will not be using gravel any more...

"Product becomes alkaline when exposed to moisture. Exposure can dry the skin,
cause alkali burns and affect the mucous membranes. Dust can irritate the eyes and upper
respiratory system. Toxic effects noted in animals include, for acute exposures, alveolar damage
with pulmonary edema."

My Alkalinity readings are not off the chart (120-180 ppm) but that fact that it says this product can effect mucus membranes makes me worry about my fish. The noted alveolar damage and pulmonary edema is also troublesome but I assume they are referring to airborne silica effecting the lungs. I suppose that silica can become suspended in the water column and effect the gills?... The specs document also mentions that the gravel is "slightly soluble in water" but it doesn't elaborate in further detail. I suppose that bad minerals or other substances could be dissolving into the water as well having a negative effect on my fish.

I had another fish die last night, and up until it died it showed no signs of being unhealthy.

So my thoughts as of now are to keep it going for a bit longer then try and transplant my plants outside after the last frost and then switch to the ever so expensive clay pellets... I hate to think of having to cycle my system again... But hey, its all a learning experience and I am still hooked on it!

Anyone have any thoughts on this? Am I overreacting?

It's funny because on the bag of gravel it says that one of its possible uses is for fish ponds.