Rains and String Algae

[mrtrumpet]

Massive rains the last two nights in the Blue Ridge. All of a sudden big blooms of string algae are on many of my stream/falls rocks. Never seen this before. Is it normal? thx

 

[Lisak1]

Yup. The rain can change the balance in your pond very quickly.

 

[Meyer Jordan]

Yup. The rain can change the balance in your pond very quickly.

Please elaborate. Rain can change the water temperature considerably over time and overcast skies can affect the Oxygen level, but I know of no other major change in other parameters that would be caused by rain even over extended periods.

 

[CometKeith]

It seems like my pond changes drastically every two days in the spring. If you have biological matter as part of your pond filtration, when your benficial bacteria gets active the string algae should totally disapear in one day.

 

[Lisak1]

Yeah - "balance" was kind of a vague word choice! Rain in our region is very acidic - if we get enough in a short period we see big pH swings. Plus runoff increases - twice we've gotten so much rain so fast that the overflow couldn't keep up and the pond breached the banks. We had a crazy algae explosion both times.

 

[Meyer Jordan]

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if we get enough in a short period we see big pH swings.

How large of a "swing" have you documented?

 

[mrtrumpet]

Maybe the acid rain (coal fired TVA plants just over the mountains) and colder temps than we've had might have done it. Temps went down into the low 40's at night where as they have been mid-50's for the past several weeks. pH may be slightly higher, but not much different than before the rains. As far the algae goes, it's nothing a little sodium percarbonate won't cure, but right now it looks kind of pretty, so I may leave it for a little while. But, in my experience, string algae begets more string algae, and I don't want that!

 

[sissy]

We have had over 6 inch's of rain and temperature went from 83 degrees down to 40 degrees and rain is over as of last night and it is back up to 87 degrees and sunny .Rained since last thursday .That is 6 days of heavy rain and I added extra crushed oyster shells preparing for all the rain .I used almost a whole bag of them from tractor supply .Peroxide to me is safer ,pour it on after you turn off the pump and wait 20 minutes or more and turn pump back on and done

 

[Meyer Jordan]

pH may be slightly higher, but not much different than before the rains.

As would be expected. Entirely too much is made of how rainfall affects the pH of a pond. For any dangerous pH swing to take place, a goodly portion of the existing pond water would have to be completely replaced with rain water and this just does not happen. For example- an 8' x 10' x 2' pond holds about 1200 gallons. 1" of rain falling on this pond (surface area of 80 sq.ft.) equals about 50 gallons. 50 gallons is 4% of the pond's total volume and this is assuming no overflow. This is not enough to impart a major pH swing.

 

[sissy]

but you have to account for pollution and runoff of any sort .I saw it on the weather channel .They talked about dust and even fire ash and how far it can travel and then rain will bring it down to the ground .Like when I get really heavy rains it overshoots my 8 inch gutters and goes straight into the pond .And with these rains we got they were heavy .My rain cage was at a little over 7 inch's .Not sure how correct it is but has to be close

 

[Lisak1]

We've seen our pH go down a full point, back in the day when we still tested. Whether that was from the actual rain or the fact that most of the mulch edging the pond ended up IN the pond is hard to say. "Run off" isn't even the right word - the pond appeared 20% bigger as the water came right up over the edge and swamped the surrounding yard. And the result was a nice green pond within 48 hours, both times. (We're expecting 3-5 inches of rain in the next few days - maybe I can document it again!)

I believe your calculations @Meyer Jordan, however we also pump our sump pump into our pond. When we get a heavy rainfall, the pump will still be going two or even three days later, running every few minutes. Our pit holds 30 gallons - if the pump runs 10 times an hour we are getting 200 gallons of water an hour in the pond (assuming the pit doesn't fill completely before the pump is triggered). That's a lot of water change over in 24 hours, not even considering the actual rainfall.

 

[Meyer Jordan]

We've seen our pH go down a full point, back in the day when we still tested. Whether that was from the actual rain or the fact that most of the mulch edging the pond ended up IN the pond is hard to say. "Run off" isn't even the right word - the pond appeared 20% bigger as the water came right up over the edge and swamped the surrounding yard. And the result was a nice green pond within 48 hours, both times. (We're expecting 3-5 inches of rain in the next few days - maybe I can document it again!)

I believe your calculations @Meyer Jordan, however we also pump our sump pump into our pond. When we get a heavy rainfall, the pump will still be going two or even three days later, running every few minutes. Our pit holds 30 gallons - if the pump runs 10 times an hour we are getting 200 gallons of water an hour in the pond (assuming the pit doesn't fill completely before the pump is triggered). That's a lot of water change over in 24 hours, not even considering the actual rainfall.

Why would you be pumping water with a known low pH into your pond? Tempting fate is an understatement!

but you have to account for pollution and runoff of any sort .I saw it on the weather channel .They talked about dust and even fire ash and how far it can travel and then rain will bring it down to the ground .Like when I get really heavy rains it overshoots my 8 inch gutters and goes straight into the pond .And with these rains we got they were heavy .My rain cage was at a little over 7 inch's .Not sure how correct it is but has to be close

Certainly there comes a tipping point where the sheer volume of water overwhelms even the best bermed pond and, Yes, organic contamination from run-off plays a role. But these are not periodically recurring rain events rather the exception.
The biggest concern with a extended period of overcast conditions, rain or no rain, is a drop on Oxygen levels due to the reduced photosynthesis of the pond's algae. More fish kills occur in the wild from low oxygen as a result of extended periods of low sunshine than for any other reason including increased acidity.
Locally we have had more than one rain event in the past where the 24 hour precipitation total was well over a foot (12 inches). Even with this, the ponds that were properly bermed showed little change in pH and those that weren't did not manifest a large swing in pH or incur any loss of fish if adequately aerated.

 

[Lisak1]

Why would you be pumping water with a known low pH into your pond? Tempting fate is an understatement!

Expensive tap water and a desire to capture as much of the free stuff as possible?

 

[sissy]

reason I have 12 airstones and reason for the home made spitter and the ball valve in the pond that helps aerate the pond .I would rather have to much air than not enough .I have seen ponds built here that were so still and not aerated and people wondered why fish died .They would tell me all the water tests were good but the pond had no aeration .