A 60% water change can cause a nutrient deficiency. It all depends on what nutrient is deficient and what the source of that nutrient is. There are 4 major sources of nutrients.
1. Fish waste
2. fetilizer
3. Substrate
4. the water source.
If the fertilizer, water source, fish waste, doesn't have enough for any of one nutrient, the substrate is the only source of the nutrient the plants need. Then each and ever water change will reduce the amount of that nutrient in the substrate and eventually it will run out and plant growth will slow and then stop.
and then the plants will die. And if the nutrient deficiency is bad enough even algae will die off.
Jtcp went 2 to 3 months with good plant growth and some algae. He now has dying plants and less algae. Seachem Flourish comeprehensive is really weak in some nutrients and we have no idea what is in his tap water. The longest I have seen anyone go in this situation is about 1 year.
Now in ocntrast if the water had the needed nutrient a 60% water change would be beneficial and would help avoid a nutrient deficiency. The best way to prevent.
The bet way to resolve this situation is to supply the missing nutrient. Without lab testing it is not possible to determine what nutrient is the problem. The other option is try and identify a better more complete fertilizer and try that. IN this case I think TNC complete fertilizer is a a good option to try..