How to maintain low TDS with water changes

[Warwick]

Hi

Im fairly new to shrimp keeping and have done a lot of reading but im stuck on how to maintain a low TDS in my shrimp tank

I hope someone can help me.

Heres my problem

I want a TDS of 150 in my aquarium and over time i let it creep up to 170. So if I do a 25% wc with DI remineralised to 150 then it will only bring it down to 165. Then if i do another the next day (which i wouldnt but in theory) it would come down to 161.25

So my understanding is that unless i do a 51% water change or more i can never lower it back to 150.

I know i could just add pure DI but obviously this would change the parameters.

So how do people do it. I appreciate any help

 

Edited March 7, 2019 by Warwick
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[jayc]

TDS creeping up from 150 to 170 in short span of time, say 1 day to 3 days, is usually due to the materials you have in the tank. It can be difficult to find. How fast are you finding TDS go from 150 to 170?

A simple test you can do is use several plastic cups and add the items in your tank along with water. Measure the TDS of the water before adding it in the cup. Start measuring TDS after 1, 2, 3, 4 days to see what is raising your TDS.

Usual suspects are substrate/gravel; filter noodles (glass or ceramic); rocks; ornaments.

TDS does rise naturally and slowly. The shrimp can handle the slow rise. But changing your parameters in a rush, like daily water changes because you are chasing an ideal TDS, is more detrimental to the shrimp than the TDS itself. So try to find the cause of the TDS rising and avoid daily water changes. On hot summers, water can evaporate faster, causing TDS to rise due to the concentration of dissolved solids in the tank which now has less water. So top up evaporated water with pure RO to bring TDS back inline to what it should be.

TDS also rises as waste is produced from the shrimp and left over food. So gravel vac occasionally can help and removing uneaten food is also a good idea. Feed less maybe.

[Warwick]

It takes about 2 weeks to go from 150 to 170 but that doesnt matter in reference to my question.

Lets say it hypothetically it takes a month or even 2 to get to 170.

Lets also say hypothetically in that time i had 0 evaporation (i do have a lid so it is fairly minimal anyway)

How can i bring it back to 150 without doing more than 50% water change if the water im using is remineralised to 150 so that the parameters stay the same?

In regards to pure water top offs i would have to do a 10% change to bring it from 170 to 153 which would change my gh from 5 to 4.5 and my kh from 2 to 1.8

So how can it be done?

[beanbag]

As you initially calculated, it can't be done unless you know exactly what is the chemical that is causing the TDS rise and remove it selectively.  For example, if you have 20 extra ppm of sodium chloride, then sorry, you can't remove it except for dilution.  But if the extra is something like nitrates, there are resins or plants that can remove it.

[Warwick]

Ok but if TDS will inevitability rise, and from what i see most people do weekly 25% water changes, that means everyone will get to the point where they must either do more than 50% change or change their parameters.

I thought maybe i do the 10% pure change and then slowly build my gh and kh back up. Which of course means the same thing in reverse - i will never get my gh and kh back to 5 and 2!

What do you guys do?

[beanbag]

You have to accept that your tank TDS will always be higher than the TDS of your input water.  Using the power of math, you can calculate if your tank rises x ppm per week, and you do y% water change every week, the equilibrium ppm will be z.

I mix up my input water to have barely lower GH than what I actually want, in order to make up for evaporation.

[jayc]

1 hour ago, Warwick said:

if TDS will inevitability rise, and from what i see most people do weekly 25% water changes, that means everyone will get to the point where they must either do more than 50% change or change their parameters.

Yep, you have found the "TDS inevitably rises" problem. A tank is a closed eco system. Waste inevitably collects and raises waste (organic or inorganic) that 10-20% water changes will never get rid of. Evaporation, food, substrate, rocks, plants, etc all contribute to the change in TDS. As the tank ages, you will never be able to get it back to ideal TDS level, because those minerals are used up, either by the beneficial bacteria, shrimps or plants, or dissolved solids are added from some other source.

A complete water (99%) water change is required to reset your water parameters. This is a good idea to perform a drastic water change half yearly. This reset the levels of Calcium, Magnesium, and removes any build up of unwanted minerals. 

I do this every 6 months +/-.  I have found this to be the ideal length of time before minerals in a closed ecosystem like a tank get completely depleted leading to moulting issues with shrimps. This big water change is when I gravel vac the substrate as well as squeeze out filter media. 

 

BTW: 150 - 170 TDS rise in 2 weeks is normal. Time for a water change.

 

Edited March 8, 2019 by jayc

[sdlTBfanUK]

JayC seems to have this covered but just thought I would join in.

I did my weekly maintenance yesterday (only do 8% each week) and took out 2 litres at TDS of 163 and as I like to aim for 160 I added new water of 128, this took the tank down to 161. So I always make the new water lower tds to compensate for any slight increase - increase in my case is due to evaporation mainly.

As regards the altering of the GH and KH, if you are using the kits with drops they only register in whole units which means your never getting an exact reading anyway to a decimal point. I use double the water in the test tube for GH so each drop added is then half a GH. All I am trying to say here is that your readings may not change for GH/KH or they might. ie if KH is really 2 and then goes down to 1.8, that will most likely only record as KH1? Hope this makes sense, but basically over all you aren't talking about much of a change so I would just concentrate on the TDS as that is a more accurate test anyway and easier to alter slowly and measurably!

Simon