I believe, or so I've been told, that hyacinths and water lettuce particularly and all plants need potasium, nitrate and phosphate. Ponds with fish produce nitrate and phosphate but do not produce potasium. I had the same problem with mine and added "Bloom and Grow" by Microbe Lift and they have started to revive and are showing signs of new growth. If you have no fish they may need all three nutrients and this product has all three but is higher in potasium. It is safe for fish, frogs and all animals.

I have 4 Koi. Where would I purchased Bloom and Grow?

The yellow color with the veining is classic chlorosis, which is almost certainly caused by an iron deficiency. I don't know anything about Grow and Bloom, but check to see if it contains iron. Potash won't hurt anything, but I don't think potash is your problem. A potash deficiency usually shows a fairly uniform olive drab color without the veining on the hyacinths. Potash deficient hyacinths usually have really long roots as well. Nitrate won't hurt anything either. I don't think you really want to add phosphate because of the algae risk.

Add iron. Find a chelated micro-nutrient mix, like Fertilome Liquid Iron. You should see improvement within a couple days. Go ahead and add some potash too. It won't hurt.

My plants aren't doing as well this year.

I have them in one of my ponds (just a 90 gallon pond) the water here has PH as high as the ocean its 8.0 think ocean is 8.2 thus close enough and they still grow great .

I found fish waste and sun are all they need and by fish I have mosquito fish so not like its a lot of waste but they did green up bit better after I added the fish

Have you added any salt to your pond at all this year?
Many plants do not grow well in a pond that has salt added to it.

Don't know what your temps are but your plants look sunburnt to me. My hyacinth did very poorly until three weeks ago when the temps finally warmed up. They had that brown look on the bulby parts. I always pull any dead plant parts off and yellow leaves on water lettuce. We get alot of temp flucs here so don't have alot of luck with those two plants. My water lilies are blooming like crazy though!

Google "chlorosis"

Thank you for all of your responses. I will do some more research. I have not added any salt to my pond.

Hi Midwester

I live in Cambridge Ontario Canada and purchased mine from "Pond's and Patio's" Too far a drive for you. You could google it and see if a there is a pond store near you that sells it or something like it. I have not had an algae bloom and was told it will not cause one as your plants will absorb it first and as long as your plants are doing well they will complete with the algae and win. However, I do have an Oase pressure filter with a UV clarifier built in so it's hard to say if that is the reason for no algae bloom.