Phosphoric acid to lower ph?

[kiky]

Recently, my friend, an arowana (scleropages formosus) hobbyist, told me that to lower ph in his pond, he has constantly been using phosphoric acid. And after all these years (4 years to be exact), there is no visible harm to the fish.

I wonder if this acid can also be used in koi pond! Any comment, please.

[MikeM]

I have some experience using phosphoric acid, but not with koi. Used with care it can be successfully employed to help alter water parameters to match the low mineral content, soft, acidic water of rainforest waterbodies. However, the phosphorous acts as a fertilizer and will contribute to algae blooms etc. It is not reliable with high alkalinity water, and results in many pH fluctuations dangerous to fish. I ceased using it long ago and substituted rainwater in which sphagnum moss had soaked for a few weeks to create soft, acidic water for aquarium species needing those conditions. [Gave them up eventually because simply too much work.]

I do not believe the water for koi should be treated to alter pH unless the pH is so high as to be wholly unsuitable. That is rarely true. If that is the case, as much as I love koi, I'd have to recommend keeping other species. In the tropics, a pond of african cichlids would be a beautiful sight ... not koi, but one can learn to appreciate other things. Eventually, the pH fluctuations will cause serious problems. Stability is more important than "perfect" pH.

[Fishbreeder]

What Mike said is true. Phosphoric acid is a commonly used source of phosphate for fish ponds used for rearing fish larvea to fry.

I'd not use it in any pond subject to any sunlight or other light source as phosphate is usually the limiting nutrient and will cause an algal bloom from hell in a nitrate rich environment.

I've found that if it is necessary to adjust pH, hydrochloric acid seems to be best as it adds "nothing" to the water but hydrogen and chloride ions.

I also agree that with most cases, stability is more important than any particular number with referrence to pH.

However, in the case of trying to bring fish into show form, then pH plays an important role with respect to the overall condition of the show animal.

Brett

[MikeM]

Brett: You should expand on "pH & show form" on the thread about finishing.

[kiky]

Thanks Mike and Brett. I'll convey this information to my friend.

Before being treated with phosphoric acid, the ph of his pond was 9.5. Is this level 'so high' that it need to be treated (well maybe with hydrochloric acid as Brett suggested), or should it be left alone as long as it is stable, as Mike said.

And for koi, what would be the maximum ph that is considered as still acceptable?

[Fishbreeder]

If the koi are still alive it must not be too high. However, that is really a bit extreme for koi.

You really need to know your other water quality parameters, especially hardness and alkalinity. This might help explain the reason for your high pH and provide some clues of how best to manage it.

This water is either very hard, salty, wierd, or very soft. If it is very soft, a little acid might be way too much. If hard, it might take quite a bit to have any effect at all. If its wierd, there is no telling what might happen. I've had experiences with all sorts, even wierd.

I would want to do what it took to bring the pH down to a more moderate level. It might be very simple or could be very complex. If I had more information I might could suggest a way to manage the situation.

Brett

[kiky]

Unfortunately Brett, other parameters have not been tested. I can only gathered the following data:
- pond size: 120 tons (concrete pond)
- fresh water is continuously supplied at a rate of 4 tons per day
- ph of fresh water is 7, with TDS of about 180 ppm

My question is, if fresh water added has a ph of 7, why it rises to 9.5 in the pond? Is this a sign of bad filter?

I'll ask to have ammonia, nitrite and nitrate, hardnes and alkalinity tested this coming few days and inform you of the result!

[MikeM]

If you mean the new water has pH of 7.0 but it rises to 9.5 in the pond, then forget about treating the water. I suspect the pond is less than a year old and the concrete is leaching. If this is the case, it will gradually improve on its own. To obtain quick improvement, your friend should read up on treating the concrete. Using a sealer might be a challenge if algae etc already getting established. I'd expect it is more practical to empty the pond & use an inexpensive mild acid (muriatic acid is often suggested) to neutralize the alkalinity on the surface of the concrete. Concrete will still leach, but more slowly.

[Bob Hart]

Kiky,

Hope you dont mind me asking, but is the fresh water's pH tested as from the tap? If it is Chlorinated and tested 'fresh' from the tap, it may affect the reading.

As an example, my tap water tested direct, has a pH of 7.6. If an amount is put into a bucket and aerated, even after an hour or so, the pH will have risen to 8.6. The aeration evaporates the Chlorine, so the true pH valve was actually 8.6.

Although 9+ is high, it may be it's true value and you could be chasing a problem which is not there at all.

Regards, Bob

[kiky]

Mike,

You are so right. My friend told me that this pond is indeed less than 0ne year old. I have informed him to have the water tested, as Brett suggested. He has brought sample of the pond water for analysis to the lab of the Health Department. Results will out in one week. And Mike, how long it will take for the ph to come down by itself, if left untreated? Since there are about 35 fishes with average size of 50 cm, it is inconvenient to empty the pond and have a muriatic acid treatment.

For Bob,

The water is from underground, from a deep well of 70 m sucked by a submersible pump. Do you have any experience with underground water?