There are a variety of papers on the topic for hydroponics (see below) using weak acid cation resins with reciculation to control pH so you don't need to constantly replace buffers or use pH up/down chemical additions either, there are also some forum threads and reddit posts, some related to marijuana hydroponics. I suspect the same approach could work for fish breeding depending on marine/fresh water.

https://www.researchgate.net/publication/11808440_Stabilizat...

https://www.tandfonline.com/doi/abs/10.1080/0190416920936436...

https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1399-3054....