Question
QUESTION: I recently lined the inside of a 10,000 gallon pond with poured concrete using Quikrete, 4" thick all around. While I am waiting for the cement to cure, I am shopping for a tinted cement sealer that would allow me to seal and color the cement all at once. Thoroseal is the brand that keeps popping up, but it isn't very specific about dyes, etc. I think a dark blue would be nice, since I won't have to look at algae sitting at the bottom. The pond is 5-6' average depth and filling and emptying just to get rid of the alkalinity of the lime left behind on new concrete just isn't an option.My koi are sitting in a large inflatable pool right now and the sooner I can transfer them to their new home, the better. What do you know about concrete, and is sealing really necessary, as I've heard? Also, I am in the habit of pressure washing the pond (previously lined with an unsightly liner) every spring, so the sealant needs to be able to withstand that as well.

ANSWER: All you want is a impervious liner.
It could be Epoxy or a PU based or FRP would do the job and would with stand the pressure you are speaking about.
The Alkalinity raises due chemistry of water not as per requirement.
If pH is balanced then the problem will not rise with normal plaster also but its not the case always hence sealer and I would recommend any one of the above.

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QUESTION: I don't understand your answer at all. I am looking for products/specific brands with which to seal the pond concrete. I was told that unless I seal it, I would have to empty, refill, wait 2 weeks, empty again, etc. Again, not an option because of size. I have no idea what PU or FRP is, guess I'll have to research that. I was hoping you had experience in concrete ponds to give me a better idea of what I need and options, if any. Not sure what you mean by the alkalinity answer. I'm not a scientist, just a dumb landscaper.

Answer
Sorry about the answer.
The pond water chemistry has to be maintained in order to prevent built up of Alkalinity in the pool.
The parameter if you observe will help you and as I cannot give the exact brand since the brands used by me would not be available in the area you are located.PU Polyurethane paint.
FRP it stands for Fibre Reinforced Plastic its a product best used for the Fish Pond.
But if for normal I advise you use Bio Filter with UV,
The test kit for all the parameter should be available with vendor who sold the fish to you. And maintain following standards:
Ammonia : NIL
Nitrite:Less than 0.3 mg/liter
Nitrate: 25-100 mg/liter
pH: 7.0- 8.0
CH: 6-12 deg CH
TH: 7 -14 deg TH