Balancing pH and N in planted tank

[OnlyGenusCaps]

So, right now I am in a bit of a tug of war. I have a lightly stocked, low-tech, heavily planted tank. I have a sizable filter. Sizable enough that between that and the plants, I have quite low N available in all forms. This has lead to a number of... Learning experiences. Right now, I'm rarely changing water as I have below detectable N in all 3 basic forms. But, when I let the water sit, I get a pH (+0.1/week) and TDS (+30ppm/week) increase. With my pH at 8.3 right now, I am not eager to let it get higher. To keep the pH and TDS down, I've been doin g weekly water changes of about 15-20% using RO. But of course then that eliminates any N I've had a chance to build up.

I've dosed with root tabs, and I'll be adding to the fertilizer to the water column soon as well (I've been reluctant to fertilize the water column because of the algae in there). But my real question what is causing the pH and TDS increase. I've only added RO (running 6.5 and 8.1ppm), have Seachem Flourite black as the substrate, bogwood, and "blue stone" rocks from a local rockyard. The only thing I can think of is the rocks are doing me in here. Unless it's the biohome in my sump? I'm reaching here.

I'd love to get thoughts from others, especially if you think there is something I am missing. Has anyone else experienced a background increase in pH and TDS? If so, what was the cause?

Thanks!

 

[Essjay]

I'm not well up in measuring TDS, but I think everything dissolved in the water adds to TDS. So things other than ammonia, nitrite, nitrate, the hardness minerals and KH will increase TDS. Things like the countless other things excreted by the fish, tannins from any wood, phosphates from fish food, and so on.

If you are concerned the rocks are causing the problem, get two tubs and fill them with water. Test both tubs straight away to confirm they give the same reading. Then put one of the rocks in one of the tubs and test every day. The tub without the rock is there as a control - any difference between the two is due to the rock. If the rocks are causing a change, it should show up in the tub after a few days.

 

[seangee]

There is no point in measuring TDS and most don't. As @Essjay says every time you add food the TDS goes up.
N is not needed in tanks so there is no need to build it up. If you have plants they will use the ammonia produced by the fish and food. That is not the only reason we change water. Personally I change 75% of the volume in each of my tanks every week, even though at any time the N readings are 0,0,0. IMO the easiest way by far to ensure a healthy tank is to change at least 50% of the water every week. Fish live in their own waste, and pheromones, hormones and bacteria are not measurable.
FWIW all my tanks are planted and the plants are all thriving.

 

[OnlyGenusCaps]

I'm not well up in measuring TDS, but I think everything dissolved in the water adds to TDS. So things other than ammonia, nitrite, nitrate, the hardness minerals and KH will increase TDS. Things like the countless other things excreted by the fish, tannins from any wood, phosphates from fish food, and so on.

If you are concerned the rocks are causing the problem, get two tubs and fill them with water. Test both tubs straight away to confirm they give the same reading. Then put one of the rocks in one of the tubs and test every day. The tub without the rock is there as a control - any difference between the two is due to the rock. If the rocks are causing a change, it should show up in the tub after a few days.

I've measured TDS in peat slurries (for another thing I do) and things like humic acids and such tent not to greatly impact it. Because it is based on electrical conductivity and back calculated, it's salts that have the largest impacts. All that said, you are completely right - I just need to toss the rocks in a bucket and follow what happens to the water. The thing is the only pieces of this I have are in the tank, and I'm less than eager to do this. I suppose I was trying to figure out if it could be anything else so I wouldn't have to pull rock to soak and wait a month. I think what you are saying is "stop being laxy and do the experiment you know you are supposed to, to figure it out"; and you'd be right. Thanks!

There is no point in measuring TDS and most don't. As @Essjay says every time you add food the TDS goes up.
N is not needed in tanks so there is no need to build it up. If you have plants they will use the ammonia produced by the fish and food. That is not the only reason we change water. Personally I change 75% of the volume in each of my tanks every week, even though at any time the N readings are 0,0,0. IMO the easiest way by far to ensure a healthy tank is to change at least 50% of the water every week. Fish live in their own waste, and pheromones, hormones and bacteria are not measurable.
FWIW all my tanks are planted and the plants are all thriving.

I suspect you and I take rather different approaches and have different understanding of plant needs. However, I am the one seeking advice, so perhaps I will find my approach is the flawed one. For now, I do greatly appreciate the different perspective. Thanks for your input!

 

[itiwhetu]

What exactly is Blue stone

 

[OnlyGenusCaps]

Excellent question! It's this stuff:

Aqua Blue | Hedberg Landscape and Masonry Supplies | Landscape and Masonry Products in Minnesota

Looks great! No idea what it might be doing to my water chemistry. Just can figure out how else 6.6 RO is becoming 8.2 aquarium water.

 

[itiwhetu]

Looks like it could have all sorts of minerals in it. If one of its components is say lime. Then you may have a problem.

 

[itiwhetu]

I have found out that it is a type of sandstone that can contain lime does that sound right to you

 

[OnlyGenusCaps]

Wow, you looked it up?! That's an amazing thing to do for a stranger. Thanks!

It gives no impression of being a sandstone. Noting "gritty" about it. I'd buy mudstone. That seems possible. Regardless, I'd agree that it has a high potential for containing something undesirable, up to and including heavy metals. I should probably just grab a piece out and put a little HCL on it and see how easily it dissolves. Then, I should get off my lazy @$$ and do what @Essjay suggested and soak a few to see what happens. If I am honest with myself those rocks are the only x factor in the tank that chould be causing the weird high pH.

 

[itiwhetu]

Go on test it, I'm interested in the result now

 

[OnlyGenusCaps]

So much pressure! I'll put it on the to do list and report back with results.

 

[mcordelia]

I wanted to comment that I also have a heavily planted tank with light stock, and I'm experiencing my pH drifting DOWN instead of up. My tap water pH ranges between 8.5 and 9, and and my water is ~12dGH. I was suprised today when I tested my pH that I had to switch to the "regular" pH test bottle because my reading bottomed out on the high range test liquid. I concluded that my pH has gone down to ~7.4 while my tap is still reading ~8.5. What I have seen more commonly made mention of is ph heading down in planted tanks, so like others have mentioned I suspect it may be the rocks or something else in your tank that is causing your pH to swing up.

Also interested to see the results of the rock pH test!!

 

[StevenF]

When plants consume nutrients they don't consume all of them equally. In my RO water tank I have to use a GH booster otherwise shrimp would die and plants wouldn't grow. GH boosters have calcium and magnesium sulfate. Plants do need calcium magnesium and sulfur to grow. But they need fare more calcium and magnesium than they do sulfur. So after plants consume what they need there is excess sulfate stays in the water. And in my aquarium this causes the PH to drop. If I don't do anything the PH will drop below 5. In your case your water probably has excess potassium. That would push the PH up. There is no way to make a fertilizer that doesn't have this problem.

The only thing you can do is to do a water change once a week. If you don't do water changes eventually all these excess minerals will push the TDS level up high enough to kill everything in the tank. Even if you don't use fertilizer and don't have plants fish food would also do the same thing. Some rocks will also do it. Water changes are not only done to control nitrogen. They are also done to stabilize PH, GH, KH, and all nutrients levels in water. We don't do water changes just to keep the nitrogen levels under control.

 

[mcordelia]

@StevenF I always appreciate your in-depth explanations. Would dosing a lot of Prime have factored into why my pH has been creeping down? I somewhat not-thinkingly converted my planted cycle into a fish-in cycle and have been dosing prime accordingly, but I know that the bottle says that it contains "hydrosulfate salts" - I don't know how these break down but conceivably there could be excess sulfur that is causing the pH to drop...?

 

[StevenF]

Would dosing a lot of Prime have factored into why my pH has been creeping down? I somewhat not-thinkingly converted my planted cycle into a fish-in cycle and have been dosing prime accordingly, but I know that the bottle says that it contains "hydrosulfate salts"

It chould but i have no experience with it. And the strength of the effect is dependent on your water chemistry. And each tank has different chemistry. Yes it is conceivable that hydrosulfates could be the cause of what you wee. But there could also be other causes. However if you consistently see this PH drop over a significant period of time you could minimize the effect by putting a sea shell in the filter. This successfully neutralized the excess acids in my tank keeping my PH at 7. It works well for tanks that have a tendency to go acid. But unfortunately a sea shells won't stop a PH rise which is what OnlyGenusCaps has. But if you can keep the PH change per week low you don't really need to do any other than a water change. But if your tank sometimes goes a couple of weeks without a water change then you probably want to do somehing in addition to regular water changes.