Plants no longer growing very well

[Willld]

I've had a planted aquarium for many years and never used to have an issue with plants. They used to grow well and I had that many I often gave some away. Nothing exotic, just common or garden ones grown without CO2 or fertilizer. Used to have florescent T8s, now have a single LED light, suitable for the size of tank on for a similar period. Same fish - guppies and various Corydoras. Same / similar filtration and same substrate.

I'm not sure if there has been a major change in our tap-water (always been fairly hard), but they'll no longer grow and get taken over by algae (which isn't a problem on rocks etc., just that the plants are growing so slowly). Not sure what has happened and I'm at a bit of a loss as to what is wrong. I'll add some pictures later to show their sorry state.

 

[Archerfish]

If all things being equal (that is nothing else has changed) then it must be the new light. It might be correct for your tank size but not sufficient for plant growth. Is it a plant light?
Getting back to everything being equal...you have guppies and has the population increased?

 

[Willld]

Light is one of these which seem to have reasonable reviews and should be OK for basic plants? Yes, the tank is probably overpopulated with guppies, but they seem healthy enough and don't appear to harm the plants directly.

 

[Archerfish]

Okay, that's why I mentioned the guppies. When I wrote my plant column, I would get similar questions and the source often turned out to be a subtle increase in fish population coupled with a new light. Your new light would be the sole suspect if nothing else at all changed but a different light and increase in fish population is a game changer. My guess is you have changes in your water parameters (higher nitrates etc.) and a light that is of a different spectrum and most likely, higher intensity than your T8's.

 

[Willld]

I try to give away some guppies when I can, but they're self perpetuating. Light is currently on for 7-8 hrs a day, at maximum brightness. What would be the best way to get some plants growing again, I don't want to go back to tubes.