Pump size for bog

[SarahT]

Boggers, you've convinced me to add a bog. I read the Bog 101 (great job), and am starting to plan. How do I figure out what size pump I can use/ should use? I have a 3200 GPH pump (not previously used) which I'd like to use to send water to the bog, but is this too forceful? (I have visions of bog pebbles erupting like Mount Vesuvius).
I'm newly in Florida and have a lined pond, roughly 1,500 gallons, 9 feet square, deep part is 40", with 12-14" planting shelves on most of the sides. I've a 22" koi, 3 large goldfish and now GF babies. Water lilies (4) are starting to grow, I have a papyrus and canna lily in pots in the water, and some floating plants. Pond gets sun 8am-1pm, then dappled shade the rest of the day from an overhanging tree (lots of falling leaves). My older pressurized canister filter with a 900 GPH pump and a 9 watt UV clarifier (new bulb) aren't doing the job any longer for filtration (green water) since this pond is bigger than the old one and lots more sun.
My plan is to add a bog on the far side of the pond, 2x8 feet, which is the most space I can fit. I don't want a loud waterfall, so the spill into the pond will be wide.
Apologies if this is overly long or I missed the bog pump section.
Thank you all, in advance for any suggestions, and for a wonderful forum.

 

[combatwombat]

Hi Sarah. The primary principle in bog building is that you want water to move through it slowly to allow the bacteria as much time as possible to convert ammonia to nitrates. I think a minimum of 5 minutes of dwell time would be a good starting point. 10 minutes or longer would be better.

At the same time, you want to have enough water moving through your filtration every hour to properly service the pond.

Let's assume you're doing a 1' deep pea gravel bog. A 2x8x1 bog filled with pea gravel would hold about 120 gallons of water or 8% of your total pond volume. That means that a single gallon of water will need to move through your filter about 12 times before the total volume of pond water has gone through filtration 100% / 8%).

To achieve 100% filtration each hour, that would leave you with a 5 min dwell time, right on the edge of what will probably work well (60 min / 12). And to achieve that, you'll want to pump into the bog at a rate of about 1500 GPH (120 gal * 12).

If you do nothing to change your design, then you can simply split the output of your 3200GPH pump and send half of it to your bog and the other half somewhere else.

If 2x8 is all the square footage you can spare, you can also do what @addy1 did and just make it deeper. If you increase to 2' depth, then the same 1500 GPH will give you a dwell time of 10 min. instead of 5.

You can also disregard all this and just wing it because almost anything you build will probably still work better than what you've got now.

 

[SarahT]

Thank you for the terrific (and kind) teaching answer. So if I use my 900 gph (I'm assuming I can discontinue my canister pressure filter?), I'll be getting closer to a longer dwell time, as long as 900 GPH is enough power to move the water into the bog and therefore out of the bog. Isn't a problem to buy another pump, either. Thanks again.

 

[mrsclem]

My bog is 2x13 and 2' deep. I run 1600gph thru it and it does great. I would keep your canister filter running till the plants in your bog get established.

 

[poconojoe]

My bog is 14 feet X 5 feet and has 12 inches of gravel.

The two 10 foot long pvc manifolds under the gravel are 2 inch in diameter.
Slits are cut 1/3 down through the pvc manifold and are spaced 1-1/2 inches apart.

My pump is a 3600 gph submersible. It sits on the other side of the pond about a foot off the bottom, probably about 18-20 feet from the bog and probably between 2&3 feet below the highest point of the outlet hose.

The flow out of the bog is a little strong after the pump grate is cleaned and the bog manifold has been flushed. After a couple weeks it does slow a bit when stuff collects on the pump.

If you think you have too much flow, add a wye after your pump with one side going to the bog and the other over another waterfall or just have it return to the pond. A ball valve on each branch will enable you to fine tune how much goes where.

But, since you have two pumps, I would try the smaller 900 gph and see what it looks like.
You can always switch it out for the bigger 3200 gph.

So, there are some factors to take into consideration.
How far and how high your pump needs to push the water. That depends on the specs of the pump.
The size of your hoses or pipes.

Hope this helps.

 

[addy1]

Mine is 26ish feet long, 4ish feet wide, 2.5 ish feet deep, my pump is 6800 gph, most going to the bog, some to the loop ponds, garden hose feed, the 1000 gallon pond slow feed, the rest to the bog. External pump.

How many gallons per hour through the bog who knows. I have a great waterfall coming out of the bog.

There is not a truly perfect way to build a bog, imho, if it works it is perfect. Mine works great! and has for 11years now

 

[SarahT]

Thank you ALL for the great input and ideas, and I'm doing some re-calculations. (just FYI - we had our first egret visit to the pond. Netting foiled the invader!)

 

[alexelite]

At the same time, you want to have enough water moving through your filtration every hour to properly service the pond.

Let's assume you're doing a 1' deep pea gravel bog. A 2x8x1 bog filled with pea gravel would hold about 120 gallons of water or 8% of your total pond volume. That means that a single gallon of water will need to move through your filter about 12 times before the total volume of pond water has gone through filtration 100% / 8%).

Hello combatwombat, I am in the process of building a pond with a bog garden and I have a question about the flow rate vs size, based on your calculation.
In your example 2x8x1 can hold 120 gallons of water if empty, when filled with pea gravel it will only hold about a quarter, and this means the water will move 4 times faster. This means water is going to spend a little more than a minute in the bog before returning to the pond.
My pond will also be around 1500 gallons, with bog gardens around 150gallons. But with added pea gravel the volume of water will be around 40 gallons. I designed with this ratio based on internet info, 10% of total volume. But if the important part is at least 5 minutes traveling time, then 3/4 of the flow should bypass the bog, or increase bog's volume by a factor of 4.

 

[Lisak1]

@alexelite - welcome to the GPF! I'd suggest you start a new post to get some answers to your question. If you want to direct a question at a member use the "@" sign and it will look like this: @combatwombat . That member will get a notification that someone has tagged them.

Good luck with your build!

 

[combatwombat]

Hey @alexelite. Good catch. You're totally right. Looks like I skipped over subtracting the volume of gravel. Not sure how I missed that. The slower the water travels through the bog, the better it will filter and polish the water. Like you've realized, though, there are tradeoffs as the slower you pump, the larger the volume of the bog has to be to achieve adequate turnover.

 

[addy1]

My bog is about 1550 gallons, subtract some head , a bit sent to another pond the rest goes into the bog. My pump is rated at 6800 gph, the bog works great

 

[GBBUDD]

I would keep using your current filter untill the bog has cycled , about a year after the bogbis up and running.
I would also keep using the 3200 gph and split it off . Send by means of shutoff valves 1500 to 2000 gph to your bog. And the remaing split goes back to the pond for circulation to push water toward your skimmer or the intake of the pump.

 

[CometKeith]

Boggers, you've convinced me to add a bog. I read the Bog 101 (great job), and am starting to plan. How do I figure out what size pump I can use/ should use? I have a 3200 GPH pump (not previously used) which I'd like to use to send water to the bog, but is this too forceful? (I have visions of bog pebbles erupting like Mount Vesuvius).
I'm newly in Florida and have a lined pond, roughly 1,500 gallons, 9 feet square, deep part is 40", with 12-14" planting shelves on most of the sides. I've a 22" koi, 3 large goldfish and now GF babies. Water lilies (4) are starting to grow, I have a papyrus and canna lily in pots in the water, and some floating plants. Pond gets sun 8am-1pm, then dappled shade the rest of the day from an overhanging tree (lots of falling leaves). My older pressurized canister filter with a 900 GPH pump and a 9 watt UV clarifier (new bulb) aren't doing the job any longer for filtration (green water) since this pond is bigger than the old one and lots more sun.
My plan is to add a bog on the far side of the pond, 2x8 feet, which is the most space I can fit. I don't want a loud waterfall, so the spill into the pond will be wide.
Apologies if this is overly long or I missed the bog pump section.
Thank you all, in advance for any suggestions, and for a wonderful forum.

Hi Sarah. When you calculate the head which involves calculating how many turns you have in your pipe and how long it is then your flow can pretty easily be reduced 20-30%. The best way to decide if your pump is okay is to do a dry run with your pump attached to your pipes in your bog before you fill it with gravel and let it pump water so you can see the flow. Also it will help you decide how many cuts to make in the pipe If you aren’t sure. My bog is the same depth as my pond and works fine at about 42 inches deep and I use a 1800 gph pump. Originally I had a smaller pump but decided to upgrade it because I felt the water flow was too low. Also there is no reason to do a water fall. You can let the pond water and bog water freely mix at the demising wall between the two as long as you have a way to keep the gravel in the bog! Close to my bog I have a waterfall pump that pushes some of the water to my bog so it’s always mixing. I actually threw some fish pellets too close to my bog today and the waterfall pump pushed the food into the bog. One of my Koi got so excited it followed the food over my limestone shelf between the two and ended in my bog which only has a few inches of water on top. He had to jump about a foot to get back in the pond but figured out how to do it!