Borates and Backwashing (watering terrestrial plants with backwash water)?

[calinb]

We have limited water from a spring at home. Summers can be long and very dry. Accordingly, I back flush our sand filter into 5 gal. buckets and kiddie pools and let it sit in the hot sun for several days. After burning off the chlorine, I siphon the water to a few trees near the pool that appear to be stressed by the dry summer. (We haven't even had any thunderstorms this summer.)

Furthermore, I have no other way to get rid of pool water other than by watering plants and trees, because we live in a forest and it will end up watering plants no matter what I do with it!

Our pool water chemistry is doing great without borates but I've been thinking about the upcoming end of season closing and how 50 ppm of borates might be a good thing to slow down algae growth over the off season. I wanted to avoid PolyQuat too. The pool will be covered with a heavy sunlight-reflective tarp but perhaps borates offer an edge.

But I started to think about our trees. PolyQuat vs. Borates on the trees. Which is worse? Do I need either, given the heavy tarp and mostly cloudy off-season days and temperatures often below freezing (2100' elevation above Peck, Idaho).

chem geek kindly posted this link, which seems to indicate our trees might suffer from adopting borates in the pool:
http://www.inchem.org/documents/ehc/ehc/ehc204.htm#SubSectionNumber:9.1.1
I found his link here:
https://www.troublefreepool.com/threads/90257-Borates-Why-and-How?p=812900&viewfull=1#post812900

Under section 9.2.2 Terrestrial we find:

Irrigation water is one of the main sources of high boron levels
resulting in toxicity in the field. Few irrigation waters contain
enough boron to injure plants directly. However, it is the continued
use and concentration in the soil as a result of evapotranspiration
that lead to the eventual toxicity problems (Gupta et al., 1985). In
waters used for irrigation, Wilcox (1958) reported a critical boron
concentration of 0.3-1.0 mg/litre for sensitive crops, such as citrus
and other fruits. Semi-tolerant crops, such as potatoes, tomatoes, and

oats, tolerate concentrations of 1-2 mg/litre; tolerant crops, such as
sugar beets, onions, and carrots, can withstand concentrations of
2-4 mg/litre.


...and it continues.

What do others think here? Backwash water is not the only source of water for the trees (even in the summer) but those critical concentrations are quite low!

Also, drainage is good around the trees so maybe the borates will be flushed and diluted by our mostly off-summer 24" of average precipitation per year. We live on a bench on a steep canyon hillside.

Thanks!

 

[ping]

For what's worth I'd skip adding borates to the water. I don't think it will help that much with preventing algae growing.

Close the pool when the water is under 60 and open early when the water is still cold. If the pool doesn't freeze over, add chlorine as needed during the winter, just use a brush to mix it up if the pump is removed.

 

[sbcpool]

Close the pool when the water is under 60 and open early when the water is still cold. If the pool doesn't freeze over, add chlorine as needed during the winter, just use a brush to mix it up if the pump is removed.

I've had good luck even without a cover when the water goes below 60, even with 0 chlorine. Myself and some others on this board have experienced that CYA disappears from the pool under these conditions, which might be a plus or a minus in your situation. I presume with no chlorine microbial decomposition of CYA.

 

[JoyfulNoise]

You have to understand that those boron levels reported are very large for soil samples. If your local soil has adequate drainage and rainfall, then there will be so much seasonal dilution from precipitation that boron will be insignificant. In fact, there are many studies that report a lack of soluble boron being more detrimental to plants than too much. Much of the soil in the US is boron deficient and that causes very interesting diseases. In palm trees, too little soil boron will manifest as palm frond with an accordion style leaf curl.

I use 50ppm borates in my pool water and I have plenty of vegetation around the pool (including citrus). My soil is heavy clay with poor drainage. The plants around my pool are very healthy and enjoy a good amount of splash out. So, if anyone was to suffer from boron soil toxicity, it would be me. And there is no evidence around my pool.

Polyquat-60 would decompose in soil an eventually wind up as nitrates and carbon compounds (carbonates and CO2). But again, the concentrations would be so low as to be insignificant.

 

[calinb]

For what's worth I'd skip adding borates to the water. I don't think it will help that much with preventing algae growing.

Close the pool when the water is under 60 and open early when the water is still cold. If the pool doesn't freeze over, add chlorine as needed during the winter, just use a brush to mix it up if the pump is removed.

Perhaps it it ain't broke, I shouldn't fix it. My pool seems to be very stable and clear as it is. I will probably disconnect the pump at closing, because then I can install a good seal on the suction side PVC pipe to keep air in the drain line. The skimmer will be above water but I really don't think the skimmer and drain ball valves seal well enough. The pool may freeze over for a time, but a typical winter here will provide me with opportunities to fold the cover back and stir in some LC too. Thanks for the tip!

I've had good luck even without a cover when the water goes below 60, even with 0 chlorine. Myself and some others on this board have experienced that CYA disappears from the pool under these conditions, which might be a plus or a minus in your situation. I presume with no chlorine microbial decomposition of CYA.

60 is the magic temp then! The pool had been closed for four years before I opened it last month. It had zero CYA. If it disappears over one winter, that's fine with me. Trichlor tabs are the cheapest source of chlorine around here so I'll just use them (plain trichlor and not the "plus" tabs) until my CYA reaches 30 and then switch to LC again. Even though I have to feed the pool a bit more trichlor until the CYA comes up, it's still cheaper than buying stabilizer too.

You have to understand that those boron levels reported are very large for soil samples. If your local soil has adequate drainage and rainfall, then there will be so much seasonal dilution from precipitation that boron will be insignificant. In fact, there are many studies that report a lack of soluble boron being more detrimental to plants than too much. Much of the soil in the US is boron deficient and that causes very interesting diseases. In palm trees, too little soil boron will manifest as palm frond with an accordion style leaf curl.

I use 50ppm borates in my pool water and I have plenty of vegetation around the pool (including citrus). My soil is heavy clay with poor drainage. The plants around my pool are very healthy and enjoy a good amount of splash out. So, if anyone was to suffer from boron soil toxicity, it would be me. And there is no evidence around my pool.

Polyquat-60 would decompose in soil an eventually wind up as nitrates and carbon compounds (carbonates and CO2). But again, the concentrations would be so low as to be insignificant.

Good to hear that borates don't seem to be a problem. Guess I should make the borate decision based on the more subjective reported merits (more sparkly and smooth feeling water) but $100+ might be a bit steep for me to justify subjective merits! Maybe next year then.

Thanks so much for the replies everyone!