A simple continuous and fail-safe water-change system

[David Cottle]

When you want to take a reading you turn the meter on, dip it in the tank water and give it a swirl and take the reading.

OK, my tap water reads 346 uS and my tank is 442. What does that say about my water?

 

[sciencefiction]

OK, my tap water reads 346 uS and my tank is 442. What does that say about my water?

The difference could be due to fertilisers, if you've added any. If not, tap and tank should read about the same after the weekly water change. The frequency of water changes should be often enough not to let any significant rise. The reading would naturally rise up till the next water change but the water changes should be enough to bring the reading back to tap water each week. I am pretty certain you'll have healthy fish that way. If you fertilise, you can take a reading after its well mixed up to get an idea what effect it has but regardless, you should bring the TDS back to tap water in the end of the week.

Basically, it doesn't matter what your tap reading is. You can't change that. My tap water reading is rather consistent within 5ppm. What matters is the rise from water change to water change.

 

[David Cottle]

The difference could be due to fertilisers, if you've added any.

I add fertilizers each morning. Will check before and after.

Don't know why tap and tank should be the same after, say, a 50% weekly water change (that I no longer do). Why wouldn't the tank after the change be somewhere in the middle of tap and the tank before a 50% change (since you're keeping half of the electrolytes)?

 

[sciencefiction]

I add fertilizers each morning. Will check before and after.

Don't know why tap and tank should be the same after, say, a 50% weekly water change (that I no longer do). Why wouldn't the tank after the change be somewhere in the middle of tap and the tank before a 50% change?

It may not be, depending on your stock level, feeding, fertilisers, etc.... But my advice is, you should make it happen if you want healthy, long lived fish 🙂

My tank's TDS barely rises week from week. I haven't dosed anything in months. It is lightly stocked. I do 50-70% water change each week. I go by the water level when I water change, and always go below what I think is 50%. In my shrimp/hillstream tank I do more like 80% weekly, fish barely have room to swim. Its a small tank so water quality is more difficult to maintain unless one does enough water changes.

 

[dw1305]

Hi all,

OK, my tap water reads 346 uS and my tank is 442. What does that say about my water?

It just says you have more salts in your tank water then your tap water.

I add fertilizers each morning.

Almost certainly the fertilizer.

Measure conductivity again next week, if it keeps creeping up over the next four weeks or so change a bit more water.

cheers Darrel

 

[sciencefiction]

I'd say roll back the tank via a couple of heavy water changes to tap water and go from there. No need to "build" up your experiments on tank water that is already roughly 65ppm over your tap measurement(if I am calculating correctly)

 

[David Cottle]

No need to "build" up your experiments on tank water that is already roughly 65ppm over your tap measurement(if I am calculating correctly)

65 ppm TDS seems consistent with EI Dosing target nutrient concentrations of NO3 5-30ppm, K 10-30ppm, CO2 30ppm, etc. The PPS-Pro solution recipe I'm using from Green Leaf Aquariums includes K2SO4 and MgSO4, contributing additional conductive "solids". These levels might seem high to you because you're not dosing?

 

[sciencefiction]

These levels might seem high to you because you're not dosing?

Yes, perhaps.
The idea is that the plants use up what one doses. In reality most people overdose and get a build up. Roll forward a few weeks/months and you could easily have 130ppm on top of tap water...then why fish don't last.... If it were me, each weak would be a starting point. If I got 65ppm more at the end of that week, I am overdosing.
The only stuff that would raise your TDS to that point is KNO3. The rest are dosed in such small amounts/ppm term wise, that they don't count. But my guess is you're not dosing 65ppm in nutrients, because one should also consider plants nitrogen consumption. So you're either dosing too much, or tank waste is building up, or both. You know, its not that easy to "water change" 65ppm completely. You'd need to do several back to back water changes to remove those extra "nutrients" ....but it is very easy building them up in the space of a week...

 

[David Cottle]

The only stuff that would raise your TDS to that point is KNO3. The rest are dosed in such small amounts/ppm term wise, that they don't count. But my guess is you're not dosing 65ppm in nutrients, because one should also consider plants nitrogen consumption. So you're either dosing too much, or tank waste is building up, or both. You know, its not that easy to "water change" 65ppm completely. You'd need to do several back to back water changes to remove those extra "nutrients" ....but it is very easy building them up in the space of a week...

The fertilizer recipe I'm using has almost as much K2SO4 as KNO3, plus 2/3 as much MgSO4, all of which will contribute to TDS, plus minor amounts of other constituents. The reason they use a seemingly odd combination of N-P-K salts is apparently to achieve NO3/PO4/K proportions of precisely 10/1/10 by weight (I checked it 🙂). I've forgotten the reason for the Mg.

I shouldn't be "building up" over the course of a week. The whole idea of continuous water change is to keep everything - wastes, nutrients, contaminants - constant at good levels.

Re an earlier comment from you about water-change efficiency, I didn't answer it very well. If I wanted to drop waste/contaminant concentrations substantially, I would do a batch water change, which is efficient for this purpose. But if I want to keep water quality steady and not ever reach high waste/contaminant levels, continuous water change is the efficient way to do this.

 

[sciencefiction]

The whole idea of continuous water change is to keep everything - wastes, nutrients, contaminants - constant at good levels.

Not really, your "continuous" water change is equivalent to a 50% water change weekly. Its up to you how to keep your tank. I personally would not take lightly 65ppm rise on top of my water as a long term solution/normal thing, unless it really stays rock solid around that measure.

I shouldn't be "building up" over the course of a week.

"Shouldn't" is doing the guessing. That's why I suggested the TDS meter in the first place. You get the "guessing" out of the equation. In fact, a lot of people out here that got TDS meters for the first times tend to measure quite higher TDS than that of their initial tap water, even double and treble amounts....They too were guessing....Some used to use nitrates tests, other went by the "heavy planting" theory....There's nothing wrong with that but neither of those methods are reliable in terms of finding out what one's water quality is.

 

[sciencefiction]

There is another thing I forgot to mention. I speak from fish's perspective. To me fish are first and foremost, plants don't matter. In fact at the moment I am not really a plant keeper unless you count what grows without any effort on my part. You may have a different point of view as many plant keepers tend to do...

When there's more nutrients in the tank, the plants will be happier. Fish health does not always correlate with plant health though....

 

[David Cottle]

I personally would not take lightly 65ppm rise on top of my water as a long term solution/normal thing, unless it really stays rock solid around that measure.

I deliberately add fertilizers every day to maintain this rise. Doesn’t everyone who doses fertilizers get such a rise? Conductivity monitoring will tell me how steady it is.

 

[sciencefiction]

I deliberately add fertilizers every day to maintain this rise. Doesn’t everyone who doses fertilizers get such a rise? Conductivity monitoring will tell me how steady it is.

Absolutely everyone gets a TDS rise at the end of the week.....The question is how much and what drives the rise, and do you do anything about it...., and what do you do about it..

 

[dw1305]

Hi all,

I've forgotten the reason for the Mg.

It is the central atom of the chlorophyll molecule.

Because of <"where you live"> you may well have magnesium in your tap water, in the UK we don't tend to.

I deliberately add fertilizers every day to maintain this rise. Doesn’t everyone who doses fertilizers get such a rise? Conductivity monitoring will tell me how steady it is.

That is it. When the plants are healthy and the tank is running well you have a datum range for conductivity.

Because I use rain-water, the duckweed index and have low nutrient tanks I use the 80 - 140 microS datum. If the tank gets below this, but the plants look healthy, I add some tap water (about 17 dKH). If the tank gets a higher, I add some more rain-water or RO. Because locally is all limestone our rain water has some dKH, presumably from dust it picks up.

If I used <"our tap water">, I'd use the same approach, but my initial datum would be much higher, because the tap water starts at about ~600 microS from all the dissolved limestone.

cheers Darrel

 

[David Cottle]

It is the central atom of the chlorophyll molecule

I knew that!! (at least, I knew it was in there somewhere 🙂) but I forgot, thanks. The caprock around here is dolomitic limestone, so there's probably enough Mg in the tap water to begin with.

Absolutely everyone gets a TDS rise at the end of the week.....The question is how much and what drives the rise, and do you do anything about it...., and what do you do about it..

I don't have an end of the week. Every day is the middle of the week in my tank. What I do about controlling TDS is purge continuously, 24/7. Don't know what else to say - we just operate our tanks differently, and we have different TDS targets. Not sure what my target, expressed as ppm TDS, is exactly - but I'll know soon.

 

[sciencefiction]

I knew that!! (at least, I knew it was in there somewhere 🙂) but I forgot, thanks. The caprock around here is dolomitic limestone, so there's probably enough Mg in the tap water to begin with.

I don't have an end of the week. Every day is the middle of the week in my tank. What I do about controlling TDS is purge continuously, 24/7. Don't know what else to say - we just operate our tanks differently, and we have different TDS targets. Not sure what my target, expressed as ppm TDS, is exactly - but I'll know soon.

I know you don't have "end of the week" but I think you misunderstand me. Your water's measure, whether in EC or TDS units, has already increased its value from base tap water. And exactly because your tank operates under "continuous" water change, if all 65ppm are from your ferts, you're way over-fertilising. What would plants need at any given time/snapshot in time?...5-10ppm Nitrates, a few ppm Potassium and the lot of the rest wouldn't exceed 5ppm, so say generously say 10- 20ppm in ferts...Your tank could easily be "polluted" right now, whether that's from in-organic fertilisers or organic ones, produced by nitrification....

 

[a1Matt]

First off, I appreciate you posting your WC setup, it looks beautifully engineered.

The pertinent point (IMO) with regards to TDS is to observe the trend, i.e. is it rising, falling or staying steady.

Then once you know that you can choose what to do next.

If it is rising, it could be either from excess ferts, fish waste or uneaten food.

One simple way to gauge it is to simply stop adding ferts for a week.

I'm sure you knew that already, so the main point of this post is to let you know that if the plants are healthy and well fed then they can go without ferts for a week without any issues (and possibly a lot longer depending on plant biomass vs fish waste and the light levels, but how much longer I wouldn't like to guess over the internet).

 

[David Cottle]

I know you don't have "end of the week" but I think you misunderstand me. Your water's measure, whether in EC or TDS units, has already increased its value from base tap water. And exactly because your tank operates under "continuous" water change, if all 65ppm are from your ferts, you're way over-fertilising. What would plants need at any given time/snapshot in time?...5-10ppm Nitrates, a few ppm Potassium and the lot of the rest wouldn't exceed 5ppm, so say generously say 10- 20ppm in ferts...Your tank could easily be "polluted" right now, whether that's from in-organic fertilisers or organic ones, produced by nitrification....

You're ignoring my earlier responses to you showing that 65ppm is consistent with EI Dosing target nutrient ranges, not even counting MgSO4 or sulphates in K2SO4 that is part of the PPS-Pro fertilizer solution recipe I use.

Following the PPS-Pro guide, I add 240 mg NO3 daily. That equates to slightly less than 2 ppm NO3 added per day in my 130L tank. 240 mg NO3/day x 7 = 1680 mg NO3/wk.
The EI Dosing guide for a 20-40 U.S. gal. tank calls for addition of 800 mg NO3 three times/wk. = 2400 mg NO3/wk, so I'm well below that.

At the same time, I'm purging 10 ml/min = 14.4L/day x 10 mg NO3/L est. = 144 mg NO3/day, i.e., I'm continuously purging more than half of what I add, so my net addition is less than 1 ppm/day. And everything appears to be stable.

The pertinent point (IMO) with regards to TDS is to observe the trend, i.e. is it rising, falling or staying steady.Then once you know that you can choose what to do next.

I've been doing that with the API nitrate test for over 3 months of steady operation, and haven't seen a rising trend. The fish are doing fine. I've just started measuring conductivity following suggestions in this thread, so I'll have additional information to track.

A nice thing about continuous water change is that it‘s largely self-regulating. If NO3 concentration starts to rise, e.g., the amount purged rises accordingly. At 15 ppm NO3 in the tank, purging will be 50% greater; at 20 ppm, purging will exceed what I'm adding (and I'm pretty sure the plants consume more than what is produced biologically). For every purge rate I choose to use, and assuming a constant rate of nutrient addition, nutrient and contaminant levels will equilibrate at levels where the amounts removed equal the net amounts generated.

 

[David Cottle]

I've calculated the TDS/EC rise that should result from adding sufficient nutrient solution to achieve my target nutrient range. My "macro" nutrient solution uses the PPS-Pro recipe, which contains the following salts in 500 ml of solution (I'm using distilled water):
KNO3 32.6g NO3 content = 32.6 x 62/101 = 20.0g
K2SO4 29.3g
KH2PO4 2.9g
MgSO4 20.2g
Total 85.0g

My target NO3 concentration is 10 - 20 ppm. The total PPS-Pro salt equivalent of 10 ppm NO3 = 10 x 85g/20g = 42.5 ppm by wt. The corresponding EC rise = 42.5/0.64 = 66.4 uS.
10 - 20 ppm NO3 = 42.5 - 85 ppm TDS
Corresponding EC rise = 66 - 133 uS
Micro nutrients are additional.

An EC rise of 100 uS puts me right in the middle of my calculated target range, equivalent to 15 ppm NO3.
Stopping fertilizer addition for two days has dropped my EC by 40 uS, to 402 uS this morning.

BBA was a vexing problem in my tank during my first (learning) year. It's completely gone under my present regimen. To borrow a phrase from one of George Farmer's videos, my fish are happy, my plants are happy,
I'm happy . As I imagine there are still some BBA spores lurking around, and I don't want to deviate too much from plant growth conditions unfavourable to BBA, I'm resuming my dosing 🙂.

(Apologies to anyone who read an unrelated message in which I was testing creating a hyperlink - still haven't figured out how to do that, at least it doesn't preview properly - then was unable to edit my test message with this message. Still learning )

 

[sciencefiction]

My target NO3 concentration is 10 - 20 ppm.

Is this concentration your weekly target or daily target? As far as I know one doses every day or every other day, in order to achieve 10-20ppm total per week. Therefore at any given time, providing your continuous water changes, you want 10-20ppm divided by 7 days? A TDS or EC measure is a snapshot in time. It is the concentration there and then and it does not get any lower than that as time goes by.....

The total PPS-Pro salt equivalent of 10 ppm NO3 = 10 x 85g/20g = 42.5 ppm by wt.

What you're calculating above is not very clear to me. You have:

20g NO3 in 500ml distilled water solution.

You want to achieve 10-20ppm concentration in the tank itself. I will assume you want that measure constant every day, not a cumulative effect....? Either way, for the purposes of calculation I assumed you want that daily....though that's to be disputed...

10ppm = 10 mg/l

If tank is 130 litres, then to achieve 10ppm NO3, you'll need 10*130/130 mg/l = 1300 mg/l = 1.3 g NO3 for your 130 litre tank.

In the given scenario you have 20g NO3 in a 500 ml solution, so you roughly need to dose 500/(20/1.3) ml to achieve 10ppm NO3, which is about 32.5 ml dose from the solution. If you spread that amount over the course of 7 days, it is 4.6 ml a day.

Do you dose 32.5 ml daily or do you dose 4.6 ml daily, or thereabouts?

The total PPS-Pro salt equivalent of 10 ppm NO3 = 10 x 85g/20g = 42.5 ppm by wt. The corresponding EC rise = 42.5/0.64 = 66.4 uS.
10 - 20 ppm NO3 = 42.5 - 85 ppm TDS
Corresponding EC rise = 66 - 133 uS

I am not sure how you arrive at the above figures? In my view:

10 ppm NO3 @ 25C is 10/0.64= 15.64 EC
20 ppm NO3 is 20/0.64 = 31. 25 EC

OK, my tap water reads 346 uS and my tank is 442. What does that say about my water?

Let's say 20ppm NO3 is your daily max amount you want to allow for in your TDS/EC reading and you have an increase from 346 to 442= 96 EC, which by the way is an increase in EC(TDS) of 27.75% !
.
For the purposes of better understanding I will use both EC and TDS values...

96 EC is the equivalent of roughly 61.44 ppm, from which at values for

20ppm NO3 - only 31.25 EC from the 96 EC rise

10ppm NO3 - only 15.64 EC from the 96 EC rise

I am pretty certain PPS-Pro recommends the 10-20ppm as the weekly measure and not daily, therefore if you are to achieve max 20ppm NO3 per week, your daily differential from base tap water to account for the daily NO3 dose, assuming plants used none of it at all, is 31.25 EC/7 days=4.46 EC on top of your base water, or your EC reading should read 346+4.46=350.46.

Which means you have 96-4.46=91.54 EC unaccounted for in you daily EC test, give and take the other ferts and plant uptake...

NO3 is the fert at highest concentration...So again, I think you're either severely overdosing or there's more than just in-organic fertiliser buildup in your tank....