I have a 180litre tank ( approx ) with 8 marble anglefish, after water changes the water pH get aroud 8.2-8.4... this is a bit high for angles right ? ... I have tried using peat balls ( From normal compost ) and i have seen it lowering to aroud 7.8 - 8.0 but It must be around 6.0-7.5. Any tips on how to lower this without harming the fish ?

Thanks for you help in advance,