How To To Properly Cure A Garden Pond Waterfall
So It's Safe For Pond Fish & Koi

I receive many emails each week from folks who have visited The-Artistic-Garden, and often their questions are something that I think "hmmm ... I ought to write an article about that!" So with that in mind, I want to share an email question, and my answer, pertaining to whether or not hypertufa could be used to construct a small garden pond waterfall and if it would be safe for the pond fish and plants.

Here's the email question and important tips that I shared with Diane ...

Hi, I'd like to know if hypertufa would be safe for constructing a small pond waterfall to use with a koi pond or is it toxic for my fish? Diane

Hello Diane:
Thank you for contacting me and I will gladly answer your questions:

Yes! Hypertufa *can be* toxic if NOT PROPERLY CURED. Due to the Portland cement that is used for a 'tufa recipe, the hypertufa ends up being very alkaline. If you have ever seen a white powdery residue on new cement, that is the free lime leaching out. This lime causes the alkalinity.

The lime is toxic to most plants and even more so to koi and pond fish! Thusly, the lime needs to be leached from the waterfall before you even think about adding in fish or aquatic plants to the pond water.

Now, if you had a planter or similar object, most crafters agree that if you submerge the cured item in a water "bath", and make sure to change the water every day, then the lime probably is leached out in about 3 days.

But you are talking about a waterfall for a garden pond -- of course this is a large object that you obviously cannot submerge. Then my suggestions (I've never attempted to build a garden pond waterfall, so please understand I am telling you what I'd do if I were to tackle this project) are the following:

1. Let the hypertufa cure properly for about a month--don't rush this step--you don't want a crumbling mess in months to come!
2. I would then fill my pond (not all the way up -- just enough to be able to nicely circulate the water -- this saves you $$ too if you have to pay for city water!) and let the water circulate over (run down) the waterfall for a day; then DRAIN OUT all the pond water (you MUST get rid of the lime that is now leaching and accumulating in the pond water) and repeat this process for at least three days.
3. REAL IMPORTANT STEP:  purchase a pH test kit for aquariums or ponds ... and test the pH level of the water! Once the pH comes into the "acceptable" range for the koi (they are VERY sensitive fish--I've owned koi for many years--they are NOT as hardy as goldfish) then if it were me ... to be on the safe side, I'd drain out all the pond water a final time ... THEN fill up my pond, use dechlorinator, etc. and let it run for another day ... then TEST the pH level again to make sure everything was pH stable. THEN I'd add in my koi.
4. I'd not rush anything about this process nor any of the steps. Erring on the safe side, rather than the "ulcerated or dead fish" side is a much better way to approach a project such as this!!

Lastly, I will assume you know about koi and how to properly integrate them into a pond, to care for them, etc. If so, then you ought to know that having a pH test kit is mandatory equipment if being a serious/concerned koi keeper :-)

I have written a number of pages about basic water chemistry and how it relates to koi. If you've not already checked out these pages on my site I encourage you to make sure to do so. (There are links at the bottom of the page that take you to more specific info on the different water chemistry levels you need to keep aware of.)

I hope this information helps you. Please make sure to read all about how to properly cure hypertufa and this info should help give you a better idea of what you need to do to successfully cure your small garden pond waterfall.

I wish you lots of success with trying this project, and if you learn how to build a garden pond waterfall ... well I think you'll be able to try your hand at just about any other hypertufa project you want to!

Thanks for contacting me.
Claudia

For more information on pond water chemistry issues, please take a look at these articles:

• Water Quality Overview: Issues & Concerns
• Healthy Pond Water for Healthy Koi & Pond Fish
• Ammonia: Toxicity Issues & How To Remedy High Levels
• Nitrites: There Is "Zero" Tolerance for Nitrite Readings
• Calculate the Gallons in Your Pond: Mathematical Formulas