weekly KH increase

[cousinkenni]

So I got a RO unit about 4 months ago and started using it to do water changes on a few of my tanks. In particular, on one of my 10gal tanks I use 100% RO water to do my 50% weekly w/c (5gal) and supplement with 1/4 tsp Equilibrium after the w/c. I also fertilize with KNO3(1/8tsp), KH2PO4(1ppm) 3X weekly and use 4ml Plant nutrition 3X weekly for the micros.

As far as I know I don't add any KH to my tank but every week the KH is back to 50ppm. When I test it about an hour after the w/c it has dropped to somewhere between 2-3 drops worth (Hagen test kit = 20-30ppm) but right before the next weekly w/c the KH has risen back up to 50ppm............Why?

Maybe this has been aswered before? Is something I'm adding during the week messing with the test kit? Do the plants actually produce something that increases the KH?

(unlike my ADA tank the GH seems to stay constant week to week)

Any information would be greatly appreciated.

Ken T.

 

[Frolicsome_Flora]

So I got a RO unit about 4 months ago and started using it to do water changes on a few of my tanks. In particular, on one of my 10gal tanks I use 100% RO water to do my 50% weekly w/c (5gal) and supplement with 1/4 tsp Equilibrium after the w/c. I also fertilize with KNO3(1/8tsp), KH2PO4(1ppm) 3X weekly and use 4ml Plant nutrition 3X weekly for the micros.

As far as I know I don't add any KH to my tank but every week the KH is back to 50ppm. When I test it about an hour after the w/c it has dropped to somewhere between 2-3 drops worth (Hagen test kit = 20-30ppm) but right before the next weekly w/c the KH has risen back up to 50ppm............Why?

Maybe this has been aswered before? Is something I'm adding during the week messing with the test kit? Do the plants actually produce something that increases the KH?

(unlike my ADA tank the GH seems to stay constant week to week)

Any information would be greatly appreciated.

Ken T.

have you calibrated your test kits? make a standard KH solution, or buy one of gregs/aqua essentials. Only then will you be able to tell exactly how much KH you have. Test kits are very hit and miss, dont take them as read.

 

[neil1973]

what substrate do you have? Many gravels etc. are not inert and contain carbonates.

 

[Tom Barr]

GH is composed of nutrients, Ca/Mg, KH can be a nutrient or not, if you have good CO2, then it should not be.

Regards,
Tom Barr

 

[cousinkenni]

Flora,

How calibrated do I really need it? This is a simple observation, and to me if I take something that has 50ppm dilute it 50% with RO water to 25ppm that seems pretty calibrated to me. I don't care about absolute values I only care about relative values and for this purpose an uncalibrated test kit will work fine. I just want to know what if anything is causing 1) the KH to increase or 2) if the KH isn't increasing what substance that is being produced in the tank causes the KH kit to be innaccurate.



Neil,

I use straight flourite




Tom,

I don't really care how much KH is in the tank, the CO2 is fine, I'm not woried about it being a nutrient. I just want to know what would cause the above increase? Any ideas would be greatly appreciated. Are there documented cases where either bacteria or plants excrete KH?

 

[Tom Barr]

I'm just saying that the GH can remain the same due to uptake by plants while the pH/KH rises..................

So if was from say CaCO3, you'd keep the same Ca/Mg GH total, but the KH would go up.

Clean everything, check the rocks etc.
Tap water changes etc as well.

As I seldom test such things unless I have basic question I want answered, such issues no longer bother me. Testing can be a disease. It can cause folks to go on long excursions to nowhere.

The Flourite might have some KH causing some material in the tank to dissolve more etc due to the slight acidic nature and low KH.

You need to make sure the test kit is accurate first.

Is there some reason inside the tank that you believe has any negative issue here?

RO water membranes need cleans, and you are at about that point.
Do not assume that it's pure water...........KH is the first thing to slip through.

That seems the most likely cause.

No, plants/bacteria consume KH generally, nor produce it unless they form hard shells of CaCO3 like macro algae, snails etc and die off fast etc......

Back flush the rO and change the prefilters.

Regards,
Tom Barr

 

[cousinkenni]

Hi Tom,

I guess the KH could be coming from the substrate? It has to be, I just thought that flourite was pretty inert..........maybe it is coming from the mulm?

What would it take to calibrate the test kit? I have RO water that turns blue as soon as I add one drop of KH solution (the TDS meter reads about 6 for the RO....the unit is not used much and pretty new). I also have 4dKH refernce solution from billionz that the kit reads properly......how much more accurate do we need this kit? If you really want I can test it using a specrotphotometer as long as you supply the wavelength that you want me to read at.......then I can do a standard curve but I don't think the kit is lying.........RO water reads as pretty much 0 and 4dKH reads as 4dKH. This is getting off topic.....to get back on topic...........



To answer your question, no I don't think the tank has any negative issue, I just made an observation now that I am using RO water and would like to know the answer.........inquisitive minds want to know

I started using RO water because I want to be able to contol as many variables as possible with my tanks so I can start doing my own tests. The less variables the better the results. Standard scientific method.

Ken T.

 

[Tom Barr]

What would it take to calibrate the test kit? I have RO water that turns blue as soon as I add one drop of KH solution (the TDS meter reads about 6 for the RO....the unit is not used much and pretty new). I also have 4dKH refernce solution from billionz that the kit reads properly......how much more accurate do we need this kit?

That sounds okay......you can dilute the ref solution in 1/2 and divide the sample 71.44ppm /2 and that will get in the precise range, then see how well the KH matches up to that.

I'm not there, so there are a number of things I cannot vouch for/see etc that might be done. Mulm will not have any, there may be a little in the Flourite perhaps, fish food, etc.

I started using RO water because I want to be able to contol as many variables as possible with my tanks so I can start doing my own tests. The less variables the better the results. Standard scientific method.

Ken T.

Well, controlling variables is one thing, seeing if those variables are actually meaningful and relevant is quite another matter. Folks wanna spend time measuring K+ and playing with that, but it's not critical.

While some obsess over one thing, another more basic issue, CO2, light, plant biomass changes through time etc occur and they attribute the effects on the nutrient rather than those other causes.

Overall, RO really does not afford you much control really as far as plant growth etc, it's more work, waste a lot of water. You can grow most anything is tap water, unless you have a rather picky list of plants, it should not matter.

This goes back decades, folks use to insist on RO, PO4 removers Silicate removers NO3 removers etc beuing the root of all evil in the tap. That was/is rubbish.

Then it was GH/KH issues, again, that proved to be rubbish with very few exception with a few species.

I've done both methods for years, if you have soft tap to start with, there's no point.

You can have plenty of control with the plant treatment, as logn as the other factors are addressed both plants should do the same except for the treatment. If less KH or GH etc is the goal, then it' is useful.

I think those arguments for RO are only good when you wanna to discuss fish, not plants. I just have done it a logn time and somewhat carefully in several cases and have not seen anything that I'd say is going to cause anyone problems.

I seldom suggest RO and general rally against it's use.
I've been that way for 25 years.

Regards,
Tom Barr

 

[Frolicsome_Flora]

Flora,

How calibrated do I really need it? This is a simple observation, and to me if I take something that has 50ppm dilute it 50% with RO water to 25ppm that seems pretty calibrated to me. I don't care about absolute values I only care about relative values and for this purpose an uncalibrated test kit will work fine. I just want to know what if anything is causing 1) the KH to increase or 2) if the KH isn't increasing what substance that is being produced in the tank causes the KH kit to be innaccurate.

You should always calibrate ALL your test kits, otherwise, you simply have no idea what the readings are, KH test kits, as with all test kits can vary greatly from kit to kit, and also they loose accuracy over time. Where your reading 25ppm, it could be 5, or it could be 40, who knows.

This is why we use known KH solution in our drop checkers, because we cant rely on the test kits to do that job for us.

So my point is.. you might be worrying about a reading that actually is very low, and thus, completely normal. I do see your point though on wanting to know whats altering it, but thats a separate issue to the point im making.

 

[cousinkenni]

Hi Flora,

I understand your point, but test kits don't alsways have to be calibrated..........there are two types of calibration.........ablsolute, which in my case is useless (although I can do it because I do have reference solutions) and relative which in my case is all that is needed..........My test kits test test 0 for RO water and 4 for 4dKH reference water......if you want I could do as Tom said and dilute the 4dKH to 2dKH.....I also have 5dkh that can be made 2.5dKH...........My point is that in my case I would never ever have to do this.

I am looking at a relative value........I take a sample of water right before the w/c and a sample right after the water change and then take the KH of the two samples at the same time. the first sample turns blue in exactly double the amount the second sample turns blue........relatively speaking, the first sample has double the amount of KH (regardless of what this KH is) as the second sample.

My simple question is what is causing this KH to double?

Tom's guess is something leeching from the substrate, I can buy that.

People on this forum are so uptight about testing and test kits.......everyone needs to relax.

Ken Takeuchi

 

[Frolicsome_Flora]

Hi Flora,
My test kits test test 0 for RO water and 4 for 4dKH reference water......

Ken Takeuchi

Thats exactly the calibration I mean, youve already done it. You didnt say that before.